How Invoice Tax Calculations Work

Source: workshop-client/src/app/invoices/invoice.item-totals.service.ts

• Xero-connected companies: tax rates summed first, then applied
• Non-Xero companies: each tax calculated separately then added
• Closed invoices return server values — no recalculation
• All rounding uses ROUND_HALF_UP with 2 decimal places
• Assembly payments use ROUND_HALF_DOWN (different from everything else)

Support scenarios

• "Tax amount is wrong" → Xero vs non-Xero calculation method difference
• "Totals changed after closing invoice" → closed invoice uses server values, not recalculated
• "1 cent discrepancy on payment" → assembly payment rounds differently