Because of the law of the 1st december 2019, we can't pay with 1 or 2 cents anymore.
We have to round the total price to the 0.05 unit.
If the customer pay without rounding values, it triggers an error.
Before the order is finalized, we add a line with a product rounding to round the total amount.

task-id: 2035010

Backport of PR: https://github.com/odoo/odoo/pull/40958
Backport of PR: https://github.com/odoo/odoo/pull/39488



closes odoo/odoo#41327

Signed-off-by: pimodoo <pimodoo@users.noreply.github.com>