I think one common feature of those rounding procedures is that they are only done for cash payments, rather than plastic, so rather than representing a monetar

I think one common feature of those rounding procedures is that they are only done for cash payments, rather than plastic, so rather than representing a monetary value, it would have to represent a payment specifically. (With knowledge of payment method and time of transaction since a lot of these rules had a start date.) Possibly a good library to extend off of this!