[FIX] point_of_sale: rouding half up gives wrong value

To Reproduce
============
- set cash rounding method to half-up with a value (1 for example)
- create a product available on pos with price (1.61$ in my example)
- on pos select this product and proceed to payment with cash
- with 2$ cash the total will be 1$ and change 1$ which is wrong

Problem
=======
- the function responsible on applying the rounding method doesn't take into
account the rounding method `"HALF-UP"`

Solution
========
- update the function to apply `"HALF-UP"` correctly

opw-3143698

closes odoo/odoo#111469

Signed-off-by: abla001 <abla@odoo.com>