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RTP and Unity calculate tax in two ways and compare: "sum then round" and "round then sum," both using bankers rounding rules.
“Sum then round” is calculated by determining the sum of the individual live line item taxes and then rounding the resulting total.
“Round then sum” is calculated by rounding the taxes at each individual line item to two decimal places, and then adding these rounded amounts for a total.
To determine whether to "add a penny," both methods are compared when deciding the tax for an RTP Order line item. If the "sum then round" value is greater than the "round then sum" value, a penny is added to one of the line item's taxes based on the “tax apply” order. Apply order is an RTP configuration assigned to dictate the priority of items for accounting if in the same order.
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