Account Invoice Custom Rounding

This module adds a tax rounding choice to invoices and to customer records, so you can decide how the total tax amount is calculated for a specific invoice or for all documents of a given contact.

• On a customer (contact) form, a new field "Tax Calculation Rounding Method" appears after the VAT field, with the options "Round per Line" and "Round Globally". It is company-dependent, so the value can differ per company, and it is not copied when duplicating a contact. If left empty, the company's own rounding method is used.
• On an invoice form, the same field is shown just before the fiscal position field. It is editable only while the invoice is in draft state; once the invoice is posted it becomes read-only. When you pick a customer on a draft invoice, the field is automatically filled from that customer's setting, or from the company setting if the customer has none.
• The chosen method is carried down to the invoice lines, so each line follows the invoice's rounding method.
• The tax computation engine uses this value when preparing and grouping tax base lines, so the tax totals on the invoice are computed with the selected rounding method.

In short, it gives finance users a per-customer and per-invoice control over tax rounding, while keeping the company default as a fallback.