A one-cent mismatch between your invoice and a validator can be enough for a rejection. The cause is usually rounding applied at different moments.
Pick a rule and keep it
Compute each line net amount, group lines by VAT rate, calculate tax once per group, then sum the groups. Rounding per line and rounding per group can differ, so use whichever your target format expects and apply it consistently.
Tips
- Work in integer minor units, such as cents, internally
- Round only when producing a document total
- Test with quantities like 3 and unit prices like 19.99
- Validate before sending, not after the rejection arrives
Our free invoice generator computes totals this way, so you can experiment with line items and see the effect immediately.