05 / FOR WEB DEVELOPERS
Taxation for web developers
Your job is to implement the business’s tax requirements accurately and make the system testable.
Two different questions
BUSINESS / TAX QUESTION
“Are we required to collect tax on this transaction?”
The business and its qualified tax professional determine obligations, registrations, classifications, and exceptions.
DEVELOPMENT QUESTION
“How does the website correctly calculate, display, collect, and record the tax the business is required to collect?”
The developer implements the approved requirements and reports gaps or ambiguous cases.
What information might the system need?
- Customer location and shipping destination
- Collect and validate the address fields the approved tax process needs. Country, region, and postal code may be inputs. An IP address alone is not a reliable shipping destination.
- Product or service type
- Map catalog items to business-approved tax categories. A physical tent, digital guide, and service may need different treatment. Do not classify products by guessing from their names.
- Applicable rules and sales channel
- Keep direct and marketplace orders distinguishable. Configure approved collection jurisdictions and any supported exemption process. International sales may need additional customer or product data.
Plan the full transaction
- Calculate. A tax service/API can apply configured rules using transaction details. Confirm what it supports; an API does not choose the business’s legal obligations.
- Display. Separate subtotal, shipping, tax, and order total. Recalculate when relevant inputs change. Distinguish estimates from final amounts.
- Collect. Validate totals on the server in a real store. Do not trust a browser-supplied tax amount. Keep service credentials out of client-side code.
- Record. Store the approved calculation result, transaction date, destination details needed for records, item classifications, channel, and who collected tax. Provide receipts and refund adjustments.
Have the business approve retention and access requirements. Collect only the personal data needed for the transaction and required records.
What happens when calculation fails?
A timeout should not silently turn tax into zero. Agree on a safe recovery path with the business, such as keeping the cart and asking the customer to retry before payment. Make the message readable by assistive technology.
A practical testing checklist
- Change the destination and verify recalculation.
- Test different approved product categories and mixed carts.
- Test direct and marketplace order imports without duplicate collection.
- Test approved international destinations and unsupported ones.
- Compare checkout, payment, receipt, and stored totals.
- Check discounts, shipping, rounding, refunds, and API failures against approved examples.
Do not hard-code assumptions. Keep tax configuration maintainable and documented. Ask for written requirements when a tax decision is unresolved.
Reference: State guidance for the business’s requirements review. Reviewed October 4, 2026.
The implementation checklist is a development exercise, not agency-mandated technical architecture.