[FIX] point_of_sale: correctly handle the rounding when the unit's rounding is set to zero
[FIX] point_of_sale: decimal precision was hardcoded to 2 in various places
[FIX] point_of_sale: some pos order fields were missing the proper decimal precision
[FIX] point_of_sale: use 'Product Price' decimal precision for product prices
[MERGE] from 8.0