[FIX] pos_cash_rounding: fix cash rounding for cash method only

- Go to Point of Sale > Configuration > Settings & enable "Cash Rounding"
- Configure POS:
  * Enable Invoicing
  * Enable "Cash Rounding" and "Only on cash methods"
  * Select 0.05 HALF-UP Rounding Method
- Start POS session
- Select a Product and change its Price to a value that should be rounded (i.e. $ 16.51)
- Select a Customer
- Proceed to Payment
- Enable Invoice
- Select Bank Payment method
- Validate
No rounding is applied as expected, but the rounding line still appears on printed Invoice.

opw-2449222

closes odoo/odoo#65317

X-original-commit: b0eb0fe0
Signed-off-by: pimodoo <pimodoo@users.noreply.github.com>
Signed-off-by: Anh Thao PHAM <kitan191@users.noreply.github.com>