Discount must be calculated before taxes

[Seb33300]

Describe the bug The way discount works is wrong. The discount should be applied before taxes calculation.

My config:

• tax at item level (tax per item enabled)
• global discount at invoice level (discount per item disabled)

Example invoice with the actual version:

• Items subtotal (without taxes) = 110 EUR
• Total taxes (10%) = 11 EUR
• Discount = 10 EUR
• Total to pay = 111 EUR

=> This is wrong because the invoice show a tax total = 11 EUR => This means the total without tax = 100 EUR => This means tax rate is 11% and not 10% as displayed...

Expected behavior

• Items subtotal (without taxes) = 110 EUR
• Discount = 10 EUR
• Total taxes (10%) = 10 EUR
• Total to pay = 110 EUR

This is how all invoicing softwares work.

See: https://www.zoho.com/ae/books/vat/faq/supply-vat/vat-with-discounts.html#:~:text=VAT%20is%20calculated%20on%20the%20discounted%20price%20of%20the%20product%2e

[Seb33300]

Same issue if I enable both tax per product & discount per product options: