there is
one thing with this merchant that is leading to more rounding:
they have 2 different 13.5% tax rates
So the code is collating the items for each rate.
For example
Suppose an order has
a €4 bottle of water at a 13.5% rate #1 and
a €4 espresso at a 13.5% rate #2
Then the tax code has to assume that these rates are for separate entities
so it calculates the tax paid separately for the water and the espresso
whereas if there was only one 13.5% rate
then it would combine them as €8 before calculating the tax.
That is
it would use a larger total which leads to less rounding
that is
twice it calculates
€4 at 13.5% as base price of €3.52 and €0.48 tax
for a total of €0.96 tax
rather than
€8 at 13.5% as base price of €7.05 and €0.95 tax
That is, with 2 separate tax rates there has to be more rounding, in this case one more rounding up by one cent whereas there would be only one rounding with one tax rate
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