[12.0] account_invoice_triple_discount

[DS-Landoo]

Hello! If all 3 discounts are used and at least 2 of them are not multiple of 10, the amount untaxed is wrongly calculated.
Examples (all of them with a product that costs 10000).

Discount 1: 5. Discount 2: 5. Discount 3: 0. Expected amount: 9025. Odoo amount: 9025. OK
Discount 1: 10. Discount 2: 10. Discount 3: 10. Expected amount: 7290. Odoo amount: 9025. OK
Discount 1: 10. Discount 2: 20. Discount 3: 3. Expected amount: 6984. Odoo amount: 6984. OK
Discount 1: 10. Discount 2: 5. Discount 3: 5. Expected amount: 8122,5. Odoo amount: 8122. NOT OK.
Discount 1: 3. Discount 2: 7. Discount 3: 2. Expected amount: 8840,58. Odoo amount: 8841. NOT OK

Expected amount was calculated with a calculator outside of Odoo. With bigger numbers than 10000 (to ensure there are no cents that could cause some weird rounding), the mistake persists. Can this be fixed? Regards!