[FIX] account: cash rounding

Fix the cash rounding displayed on accounting documents such as customer invoices, credit notes, vendor bills and vendor refunds. The amount that was computed was incorrect in most case. The only case that was working was the customer invoice when using the company currency. The PR address the issue of cash rounding for all account move type and when using foreign currencies as well.

Steps to Reproduce
 - Activate Cash Roundings.
 - Create a half-up cash rounding with a precision of 1.
 - Create a new bill with a pre-tax amount of 378 and a tax rate of 15%
 - Apply the cash rounding to the bill and save.
 - Review the "Total Rounded" value.

Expected Results:
The 'Total Rounded' value should be 435.00

Actual Results:
The displayed 'Total Rounded' value is 434.40

opw-3235723
opw-3236011
opw-3277942
opw-3271713

task-3257577

closes odoo/odoo#119545

Signed-off-by: William André (wan) <wan@odoo.com>
Co-authored-by: Nshimiyimana Serge Séna <sesn@odoo.com>