Money should be represented in the base unit, for dollars that is cents. So for your sum fields it should be sum_in_base_units = 859 not 8.59. Decimal can lose accuracy as you move around systems, it's most safe to just use base units.
Could you please provide an example? Given that Decimals are simplistically represented as a tuple (sign, digits, exponent), I don't see how it's less accurate than an int.
((.1)*3)/3
https://docs.python.org/3/library/decimal.html?highlight=dec...