Tax System

1. Overview

Property	Value
Status	Stable (canonical pricing input)
Owner	pricing-team
Services	`TaxSetService` (CRUD), `PricingTaxCalculatorService` (v1), `TaxCalculatorService` (v2)
Controllers / Routes	`TaxController` `/taxes`, `TaxSetController` `/tax-sets`, `TaxTypeController` `/tax-types`
Depends on	`Tax`, `TaxSet`, `TaxType` schemas (`@nx/core`)

Manages tax calculation through TaxSets (container per variant or merchant), Taxes (percentage / fixed / per-unit entries), and TaxTypes (system or merchant-scoped categories like VAT). Taxes apply in priority order with temporal windows, inclusive/exclusive calc, compound tax-on-tax, quantity conditions, and order-level taxes for merchant-scoped sets.

Service catalogue and identity card: see Pricing Service index. REST reference: live at /v1/api/pricing/doc/openapi.json.

2. Data Model

2.1. Tax Modes

Mode	percentage	amount	Calculation
Percentage	set (e.g. `0.1`)	null	`tax = taxableAmount × percentage`
Fixed	null	set (e.g. `5000`)	`tax = amount`
Combined	set	set	`tax = (taxableAmount × percentage) + amount`

2.2. TaxType Scoping

Scope	merchantId	Description
System	null	Platform-wide tax types (VAT, GST) — from seeded data
Merchant	set	Custom tax types created by a specific merchant

2.3. Inclusive vs Exclusive Taxes

Type	`isInclusive`	Behavior
Exclusive	`false` (default)	Tax added on top of price — increases total
Inclusive	`true`	Tax embedded in price — back-calculated, does not increase total

Inclusive back-calculation formulas:

Mode	Formula
Percentage	`taxAmount = price − (price / (1 + rate))`
Fixed amount	`taxAmount = fixedAmount` (deducted from price, not additional)

Note: Inclusive taxes only apply at ITEM scope.

2.4. Tax Scope

Each tax has a scope field that controls where it is applied:

Scope	Applied to	Allowed on
`ITEM` (default)	Each product variant's subtotal	Any TaxSet
`ORDER`	Total order subtotal after all items are priced	Merchant TaxSets only

Constraint: ORDER-scoped taxes must be exclusive (isInclusive = false). The system throws a validation error if this rule is violated.

2.5. Tax Behavior Flags

Field	Type	Default	Description
`isInclusive`	boolean	`false`	Tax embedded in price (inclusive) or added on top (exclusive)
`isCompound`	boolean	`true`	Compounds on cumulative tax from previous priority groups
`shouldApplyOnDiscounted`	boolean	`true`	Use discounted subtotal as base (`true`) or original subtotal (`false`)
`scope`	`ITEM` \| `ORDER`	`ITEM`	Whether applied at item level or order level
`minQuantity`	integer?	null	Skip this tax if item quantity is below this threshold
`maxQuantity`	integer?	null	Skip this tax if item quantity exceeds this threshold

2.6. Quantity-Based Conditions

Taxes can be conditionally skipped based on the order quantity:

Condition	Outcome
`minQuantity` set and `quantity < minQuantity`	Tax is skipped
`maxQuantity` set and `quantity > maxQuantity`	Tax is skipped
Neither set	Tax always applies

3. Tax Calculation Flow

3.1. Calculation Result

typescript

interface TaxCalculationResult {
  taxSetId: string;
  totalTax: string;                // Sum of all applied exclusive taxes
  appliedTaxes: AppliedTaxResponse[];
}

interface AppliedTaxResponse {
  taxId: string;
  amount: string;                  // Individual tax amount
  taxableBase: string;             // Base amount used for calculation
  taxTypeId: string;
  isInclusive: boolean;            // Whether the tax is inclusive
  isVat: boolean;                  // true if taxType.type === 'VAT'
  isCompound: boolean;             // Whether the tax compounds on previous groups
}

3.2. Order-Level Taxes

After all item-level taxes are calculated, the system applies order-level taxes when a merchantId is provided in the context:

OrderTaxesResponse structure:

typescript

interface OrderTaxesResponse {
  totalOrderTax: string;
  totalExclusiveOrderTax: string;
  totalInclusiveOrderTax: string;    // Always "0.0000" — ORDER taxes must be exclusive
  appliedOrderTaxes: AppliedTaxResponse[];
}

Note: totalInclusiveOrderTax is always "0.0000" because ORDER-scoped taxes are required to be exclusive (isInclusive = false).

4. Automatic VAT Setup

When a product variant is created, the tax system automatically creates a TaxSet with default 10% VAT:

5. Repository Operations

5.1. TaxRepository

Method	Description
`findActivated()`	Load taxes by taxSetId, filter by effectiveDate, order by priority
`findByTaxTypeId()`	Find taxes using a specific tax type
`findFutureTaxes()`	Find taxes with effectiveFrom in the future
`findExpiredTaxes()`	Find taxes with effectiveTo in the past

5.2. TaxSetRepository

Method	Description
`findActivated()`	Find activated TaxSet for product variant (strict/non-strict)
`findActiveTaxSetByPrincipal()`	Find by principalId + principalType with taxes included
`deactivateAllForPrincipal()`	Deactivate all TaxSets before activating new one

5.3. TaxTypeRepository

Method	Description
`findSystemTaxTypes()`	System types (merchantId = null)
`findByMerchantId()`	Merchant-specific types
`findAvailableTaxTypes()`	System + merchant types combined

6. Controller API

TaxController /taxes and TaxTypeController /tax-types are standard CRUD. TaxSetController /tax-sets adds a custom PATCH /{id}/aggregate (update set + its taxes in one call). Full request/response reference is rendered live from /v1/api/pricing/doc/openapi.json — not hand-maintained here.

7. Practical Examples

7.1. Scenario 1: Single Percentage Tax (VAT)

Business Rule: "Apply 10% VAT to all products"

Step 1: Create Tax Set (Automatic on Product Variant Creation)

When a product variant is created, the system automatically creates:

TaxSet with ACTIVATED status
Default VAT tax with percentage: 0.1 (10%)

Step 2: Calculate Tax

typescript

// Internal API call from PricingService
const result = await pricingTaxCalculatorService.calculateTax({
  productVariantId: 'pv-001',
  taxableAmount: '100000',  // Base price after discount
  context: {
    traceId: 'trace-001',
    calculatingAt: '2026-02-25T10:00:00Z'
  }
});

Result:

json

{
  "taxSetId": "taxset-001",
  "totalTax": "10000.0000",
  "appliedTaxes": [
    {
      "taxId": "tax-vat-001",
      "amount": "10000.0000"
    }
  ]
}

Calculation: 100,000 × 0.1 = 10,000

7.2. Scenario 2: Fixed Amount Tax (Service Fee)

Business Rule: "Add 5,000 VND service fee to all purchases"

Step 1: Create Service Fee Tax

http

POST /taxes
Content-Type: application/json
Authorization: Bearer <token>

{
  "taxSetId": "taxset-001",
  "taxTypeId": "taxtype-service-fee",
  "amount": "5000",
  "percentage": null,
  "effectiveFrom": "2026-02-01T00:00:00Z",
  "effectiveTo": null,
  "priority": 1,
  "status": "ACTIVATED"
}

Step 2: Calculate Tax with VAT + Service Fee

typescript

const result = await pricingTaxCalculatorService.calculateTax({
  productVariantId: 'pv-001',
  taxableAmount: '100000',
  context: { traceId: 'trace-002' }
});

Result:

json

{
  "taxSetId": "taxset-001",
  "totalTax": "15000.0000",
  "appliedTaxes": [
    {
      "taxId": "tax-vat-001",
      "amount": "10000.0000"
    },
    {
      "taxId": "tax-service-fee-001",
      "amount": "5000.0000"
    }
  ]
}

Calculation:

VAT: 100,000 × 0.1 = 10,000
Service Fee: 5,000 (fixed)
Total: 10,000 + 5,000 = 15,000

7.3. Scenario 3: Combined Tax (Percentage + Fixed)

Business Rule: "Apply 8% luxury tax + 10,000 VND environmental fee on premium items"

Step 1: Create Combined Tax

http

POST /taxes
Content-Type: application/json

{
  "taxSetId": "taxset-premium-001",
  "taxTypeId": "taxtype-luxury",
  "percentage": "0.08",
  "amount": "10000",
  "effectiveFrom": "2026-01-01T00:00:00Z",
  "priority": 2,
  "status": "ACTIVATED"
}

Step 2: Calculate Tax (VAT + Luxury + Environmental)

typescript

const result = await pricingTaxCalculatorService.calculateTax({
  productVariantId: 'pv-premium-001',
  taxableAmount: '500000',
  context: { traceId: 'trace-003' }
});

Result:

json

{
  "taxSetId": "taxset-premium-001",
  "totalTax": "100000.0000",
  "appliedTaxes": [
    {
      "taxId": "tax-vat-001",
      "amount": "50000.0000"
    },
    {
      "taxId": "tax-luxury-001",
      "amount": "50000.0000"
    }
  ]
}

Calculation:

VAT (priority 0): 500,000 × 0.1 = 50,000
Luxury + Environmental (priority 2): (500,000 × 0.08) + 10,000 = 40,000 + 10,000 = 50,000
Total: 50,000 + 50,000 = 100,000

7.4. Scenario 4: Tax-Inclusive vs Tax-Exclusive Pricing

Business Rule: "Display price includes VAT (tax-inclusive), but calculate tax separately for reporting"

Tax-Exclusive Approach (Current Implementation):

typescript

// 1. Calculate fare (base price)
const fareResult = await pricingFareCalculatorService.selectFare({
  productVariantId: 'pv-001',
  context: { quantity: '1' }
});
// fareResult.selectedFare.amount = '100000'

// 2. Calculate tax on fare amount
const taxResult = await pricingTaxCalculatorService.calculateTax({
  productVariantId: 'pv-001',
  taxableAmount: '100000',  // Use fare amount as taxable base
  context: { traceId: 'trace-004' }
});
// taxResult.totalTax = '10000'

// 3. Final price
const finalPrice = {
  subtotal: '100000',      // Pre-tax amount
  tax: '10000',            // Tax amount
  total: '110000'          // Customer pays this
};

Tax-Inclusive Approach (Reverse Calculation):

typescript

// Given: Tax-inclusive price = 110,000 VND (includes 10% VAT)
// Calculate: Tax amount and pre-tax amount

const taxInclusivePrice = 110000;
const vatRate = 0.1;

// Reverse formula: preTaxAmount = inclusivePrice / (1 + vatRate)
const preTaxAmount = taxInclusivePrice / (1 + vatRate);
// preTaxAmount = 110,000 / 1.1 = 100,000

const taxAmount = taxInclusivePrice - preTaxAmount;
// taxAmount = 110,000 - 100,000 = 10,000

const breakdown = {
  displayPrice: '110000',   // What customer sees
  subtotal: '100000',       // Pre-tax amount
  tax: '10000',             // Tax amount
  total: '110000'           // Same as display price
};

7.5. Scenario 5: Priority-Based Tax Ordering

Business Rule: "Apply taxes in specific order: VAT (priority 0) → Service fee (priority 1) → Luxury tax (priority 2)"

Step 1: Create Taxes with Different Priorities

http

# VAT (highest priority)
POST /taxes
{
  "taxSetId": "taxset-001",
  "taxTypeId": "taxtype-vat",
  "percentage": "0.1",
  "priority": 0,
  "status": "ACTIVATED"
}

# Service Fee (medium priority)
POST /taxes
{
  "taxSetId": "taxset-001",
  "taxTypeId": "taxtype-service",
  "amount": "5000",
  "priority": 1,
  "status": "ACTIVATED"
}

# Luxury Tax (lowest priority)
POST /taxes
{
  "taxSetId": "taxset-001",
  "taxTypeId": "taxtype-luxury",
  "percentage": "0.05",
  "priority": 2,
  "status": "ACTIVATED"
}

Step 2: Calculate Tax (Applied in Priority Order)

typescript

const result = await pricingTaxCalculatorService.calculateTax({
  productVariantId: 'pv-001',
  taxableAmount: '200000',
  context: { traceId: 'trace-005' }
});

Result:

json

{
  "taxSetId": "taxset-001",
  "totalTax": "35000.0000",
  "appliedTaxes": [
    {
      "taxId": "tax-vat-001",
      "amount": "20000.0000"
    },
    {
      "taxId": "tax-service-001",
      "amount": "5000.0000"
    },
    {
      "taxId": "tax-luxury-001",
      "amount": "10000.0000"
    }
  ]
}

Calculation (in priority order):

VAT (priority 0): 200,000 × 0.1 = 20,000
Service Fee (priority 1): 5,000 (fixed)
Luxury Tax (priority 2): 200,000 × 0.05 = 10,000
Total: 20,000 + 5,000 + 10,000 = 35,000

Note: Same-priority taxes share the same cumulative base. Taxes with isCompound = true compound on the cumulative tax from all lower-priority groups. See Scenario 7.10 for a full example.

7.6. Scenario 6: Temporal Tax Changes (Tax Rate Increase)

Business Rule: "VAT increases from 10% to 12% starting April 1, 2026"

Step 1: Update Existing VAT Tax to Expire

http

PUT /taxes/tax-vat-001
Content-Type: application/json

{
  "effectiveTo": "2026-03-31T23:59:59Z"
}

Step 2: Create New VAT Tax with Future Effective Date

http

POST /taxes
Content-Type: application/json

{
  "taxSetId": "taxset-001",
  "taxTypeId": "taxtype-vat",
  "percentage": "0.12",
  "effectiveFrom": "2026-04-01T00:00:00Z",
  "effectiveTo": null,
  "priority": 0,
  "status": "ACTIVATED"
}

Step 3: Calculate Tax Before Transition (March 30, 2026)

typescript

const resultBefore = await pricingTaxCalculatorService.calculateTax({
  productVariantId: 'pv-001',
  taxableAmount: '100000',
  context: {
    traceId: 'trace-006',
    calculatingAt: '2026-03-30T10:00:00Z'
  }
});

Result:

json

{
  "taxSetId": "taxset-001",
  "totalTax": "10000.0000",
  "appliedTaxes": [
    {
      "taxId": "tax-vat-001",
      "amount": "10000.0000"
    }
  ]
}

Calculation: 100,000 × 0.1 = 10,000 (old rate)

Step 4: Calculate Tax After Transition (April 2, 2026)

typescript

const resultAfter = await pricingTaxCalculatorService.calculateTax({
  productVariantId: 'pv-001',
  taxableAmount: '100000',
  context: {
    traceId: 'trace-007',
    calculatingAt: '2026-04-02T10:00:00Z'
  }
});

Result:

json

{
  "taxSetId": "taxset-001",
  "totalTax": "12000.0000",
  "appliedTaxes": [
    {
      "taxId": "tax-vat-002",
      "amount": "12000.0000"
    }
  ]
}

Calculation: 100,000 × 0.12 = 12,000 (new rate)

7.7. Scenario 7: Merchant-Specific Custom Tax

Business Rule: "Merchant 'ABC Corp' adds custom 2% handling fee to their products"

Step 1: Create Merchant-Specific Tax Type

http

POST /tax-types
Content-Type: application/json
Authorization: Bearer <merchant-abc-token>

{
  "type": "HANDLING_FEE",
  "name": "ABC Handling Fee",
  "merchantId": "merchant-abc-001",
  "status": "ACTIVATED"
}

Response:

json

{
  "id": "taxtype-abc-handling",
  "type": "HANDLING_FEE",
  "merchantId": "merchant-abc-001",
  "status": "ACTIVATED"
}

Step 2: Add Custom Tax to Product Variant

http

POST /taxes
Content-Type: application/json

{
  "taxSetId": "taxset-abc-product-001",
  "taxTypeId": "taxtype-abc-handling",
  "percentage": "0.02",
  "priority": 3,
  "status": "ACTIVATED"
}

Step 3: Calculate Tax (System VAT + Merchant Handling Fee)

typescript

const result = await pricingTaxCalculatorService.calculateTax({
  productVariantId: 'pv-abc-001',
  taxableAmount: '150000',
  context: { traceId: 'trace-008' }
});

Result:

json

{
  "taxSetId": "taxset-abc-product-001",
  "totalTax": "18000.0000",
  "appliedTaxes": [
    {
      "taxId": "tax-vat-001",
      "amount": "15000.0000"
    },
    {
      "taxId": "tax-abc-handling-001",
      "amount": "3000.0000"
    }
  ]
}

Calculation:

System VAT (priority 0): 150,000 × 0.1 = 15,000
Merchant Handling Fee (priority 3): 150,000 × 0.02 = 3,000
Total: 15,000 + 3,000 = 18,000

7.8. Scenario 8: Error Handling - Invalid Tax Configuration

Business Rule: "Tax MUST have either percentage OR amount (or both)"

Invalid Tax Creation Attempt:

http

POST /taxes
Content-Type: application/json

{
  "taxSetId": "taxset-001",
  "taxTypeId": "taxtype-invalid",
  "percentage": null,
  "amount": null,
  "status": "ACTIVATED"
}

Calculation Attempt:

typescript

try {
  const result = await pricingTaxCalculatorService.calculateTax({
    productVariantId: 'pv-001',
    taxableAmount: '100000',
    context: { traceId: 'trace-009' }
  });
} catch (error) {
  console.error(error);
}

Error Response:

json

{
  "statusCode": 500,
  "message": "[PricingTaxCalculatorService][_validateTaxConfiguration] Invalid tax configuration: tax must have either percentage or amount value | Tax ID: tax-invalid-001 | Tax Set ID: taxset-001",
  "details": {
    "taxId": "tax-invalid-001",
    "taxSetId": "taxset-001",
    "percentage": null,
    "amount": null
  }
}

7.9. Scenario 9: Inclusive VAT

Business Rule: "Product is priced at 110,000 VND including 10% VAT — extract the embedded tax for reporting"

The tax has isInclusive: true and percentage: 0.1. The system back-calculates the embedded tax without increasing the total.

Tax configuration:

http

POST /taxes
Content-Type: application/json

{
  "taxSetId": "taxset-inclusive-001",
  "taxTypeId": "taxtype-vat",
  "percentage": "0.1",
  "isInclusive": true,
  "priority": 0,
  "status": "ACTIVATED"
}

Calculate tax on the inclusive price:

typescript

const result = await pricingTaxCalculatorService.calculateTax({
  productVariantId: 'pv-inclusive-001',
  taxableAmount: '110000',  // Display price (already includes VAT)
  context: { traceId: 'trace-009' }
});

Result:

json

{
  "taxSetId": "taxset-inclusive-001",
  "totalTax": "0.0000",
  "appliedTaxes": [
    {
      "taxId": "tax-vat-inclusive-001",
      "amount": "10000.0000",
      "taxableBase": "110000.0000",
      "isInclusive": true,
      "isVat": true,
      "isCompound": true
    }
  ]
}

Calculation: 110,000 − (110,000 / (1 + 0.1)) = 110,000 − 100,000 = 10,000

Important: totalTax is 0 because inclusive taxes do NOT add to the total — the tax is already embedded in the display price. The amount in appliedTaxes is provided for reporting/breakdown purposes only.

7.10. Scenario 10: Compound Tax (Tax-on-Tax)

Business Rule: "Apply 10% VAT (priority 0), then 2% service charge on the price including VAT (priority 1, compounded)"

Tax	Priority	Rate	`isCompound`
VAT	0	10%	`true`
Service Charge	1	2%	`true`

Tax configurations:

http

# VAT — priority 0
POST /taxes
{
  "taxSetId": "taxset-compound-001",
  "taxTypeId": "taxtype-vat",
  "percentage": "0.1",
  "isCompound": true,
  "priority": 0,
  "status": "ACTIVATED"
}

# Service Charge — priority 1, compounds on VAT
POST /taxes
{
  "taxSetId": "taxset-compound-001",
  "taxTypeId": "taxtype-service",
  "percentage": "0.02",
  "isCompound": true,
  "priority": 1,
  "status": "ACTIVATED"
}

Calculate compound tax:

typescript

const result = await pricingTaxCalculatorService.calculateTax({
  productVariantId: 'pv-compound-001',
  taxableAmount: '100000',
  context: { traceId: 'trace-010' }
});

Result:

json

{
  "taxSetId": "taxset-compound-001",
  "totalTax": "12200.0000",
  "appliedTaxes": [
    {
      "taxId": "tax-vat-001",
      "amount": "10000.0000",
      "taxableBase": "100000.0000",
      "isInclusive": false,
      "isVat": true,
      "isCompound": true
    },
    {
      "taxId": "tax-service-001",
      "amount": "2200.0000",
      "taxableBase": "110000.0000",
      "isInclusive": false,
      "isVat": false,
      "isCompound": true
    }
  ]
}

Calculation (compound algorithm):

Priority 0 — VAT: taxableBase = 100,000 (base, no prior cumulative) → tax = 100,000 × 0.1 = 10,000 → cumulativeTax = 10,000
Priority 1 — Service Charge: isCompound = true → taxableBase = 100,000 + 10,000 = 110,000 → tax = 110,000 × 0.02 = 2,200
Total: 10,000 + 2,200 = 12,200

7.11. Scenario 11: Order-Level Tax (Merchant Service Fee)

Business Rule: "Merchant applies a 1% platform service fee on the full order subtotal after all item taxes"

The merchant has a TaxSet with an ORDER-scoped tax. After all items are priced, the system calculates this fee on the order subtotal.

Merchant TaxSet tax configuration:

http

POST /taxes
Content-Type: application/json

{
  "taxSetId": "taxset-merchant-order-001",
  "taxTypeId": "taxtype-platform-fee",
  "percentage": "0.01",
  "scope": "ORDER",
  "isInclusive": false,
  "priority": 0,
  "status": "ACTIVATED"
}

Simulation context with merchantId:

typescript

const result = await simulationService.calculate({
  items: [/* ... */],
  context: {
    merchantId: 'merchant-abc-001',   // Triggers order-level tax lookup
    traceId: 'trace-011'
  }
});

Order-level tax result (SimulationCalculateResponse.orderTaxes):

json

{
  "totalOrderTax": "5000.0000",
  "totalExclusiveOrderTax": "5000.0000",
  "totalInclusiveOrderTax": "0.0000",
  "appliedOrderTaxes": [
    {
      "taxId": "tax-platform-fee-001",
      "amount": "5000.0000",
      "taxableBase": "500000.0000",
      "isInclusive": false,
      "isVat": false,
      "isCompound": true
    }
  ]
}

Calculation: orderSubtotal (500,000) × 0.01 = 5,000

Note: totalInclusiveOrderTax is always "0.0000" because ORDER-scoped taxes must be exclusive by design.

Pricing Service — Package overview
Fare System — Fare calculation
Cost Tracking — Cost management
Promotions — Promotion system

Client Guide

Providers

Invoice Types

Tax System ​

1. Overview ​

2. Data Model ​

2.1. Tax Modes ​

2.2. TaxType Scoping ​

2.3. Inclusive vs Exclusive Taxes ​

2.4. Tax Scope ​

2.5. Tax Behavior Flags ​

2.6. Quantity-Based Conditions ​

3. Tax Calculation Flow ​

3.1. Calculation Result ​

3.2. Order-Level Taxes ​

4. Automatic VAT Setup ​

5. Repository Operations ​

5.1. TaxRepository ​

5.2. TaxSetRepository ​

5.3. TaxTypeRepository ​

6. Controller API ​

7. Practical Examples ​

7.1. Scenario 1: Single Percentage Tax (VAT) ​

7.2. Scenario 2: Fixed Amount Tax (Service Fee) ​

7.3. Scenario 3: Combined Tax (Percentage + Fixed) ​

7.4. Scenario 4: Tax-Inclusive vs Tax-Exclusive Pricing ​

7.5. Scenario 5: Priority-Based Tax Ordering ​

7.6. Scenario 6: Temporal Tax Changes (Tax Rate Increase) ​

7.7. Scenario 7: Merchant-Specific Custom Tax ​

7.8. Scenario 8: Error Handling - Invalid Tax Configuration ​

7.9. Scenario 9: Inclusive VAT ​

7.10. Scenario 10: Compound Tax (Tax-on-Tax) ​

7.11. Scenario 11: Order-Level Tax (Merchant Service Fee) ​

8. Related Documentation ​

Tax System

1. Overview

2. Data Model

2.1. Tax Modes

2.2. TaxType Scoping

2.3. Inclusive vs Exclusive Taxes

2.4. Tax Scope

2.5. Tax Behavior Flags

2.6. Quantity-Based Conditions

3. Tax Calculation Flow

3.1. Calculation Result

3.2. Order-Level Taxes

4. Automatic VAT Setup

5. Repository Operations

5.1. TaxRepository

5.2. TaxSetRepository

5.3. TaxTypeRepository

6. Controller API

7. Practical Examples

7.1. Scenario 1: Single Percentage Tax (VAT)

7.2. Scenario 2: Fixed Amount Tax (Service Fee)

7.3. Scenario 3: Combined Tax (Percentage + Fixed)

7.4. Scenario 4: Tax-Inclusive vs Tax-Exclusive Pricing

7.5. Scenario 5: Priority-Based Tax Ordering

7.6. Scenario 6: Temporal Tax Changes (Tax Rate Increase)

7.7. Scenario 7: Merchant-Specific Custom Tax

7.8. Scenario 8: Error Handling - Invalid Tax Configuration

7.9. Scenario 9: Inclusive VAT

7.10. Scenario 10: Compound Tax (Tax-on-Tax)

7.11. Scenario 11: Order-Level Tax (Merchant Service Fee)

8. Related Documentation