How do you handle HST/GST/PST/QST across provinces in a single Magento store?

Multi-province tax is one of the most under-estimated Toronto-rebuild scopes. Five rule sets matter: (1) HST 13% Ontario, combined GST 5% + provincial 8%, charged on most B2C goods/services shipped to Ontario; (2) HST 15% Maritimes, NS, NB, NL, PEI; (3) GST 5% + PST in BC (12% combined), SK (11% combined), MB (12% combined); (4) QST 14.975% in Quebec (GST 5% + QST 9.975%); (5) GST 5% only in Alberta, NWT, Nunavut, Yukon. Plus place-of-supply rules, for digital goods, tax is based on the buyer's billing address; for physical goods, on the ship-to address; for services, more complex. Exempt categories matter too, basic groceries, prescription drugs, most health services are zero-rated, but the exemption rules differ between GST/HST and provincial PST in BC / SK / MB. We wire this into Magento via Vertex Cloud O Series or Avalara AvaTax Canada (or TaxJar for smaller stores) with real-time per-line-item calculation, point-of-supply rounding, exempt-category handling, and CRA / Revenu Québec audit-ready invoice templates. For B2B sellers we also wire customer GST/HST number validation so out-of-province B2B can be zero-rated correctly.