[FIX] point_of_sale,pos_cash_rounding: fix change error popup on checkout

Configure your POS with bank payment method only
Make a sale with rounding necessary (i.e. 1,29€)
The amount will be rounded. Go through the payment screen.

Error message will appear because no payment methods available is
capable of handling the change, but this is not necessary since we are
rounding.

Splitting the code to add a more specific condition in pos_cash_rounding
fix the issue

opw-2239946

closes odoo/odoo#50216

X-original-commit: 6131534da2d3a3bf75529b32f2061d58e925b365
Signed-off-by: Nicolas Lempereur (nle) <nle@odoo.com>