Perhaps it is an "abstraction bug" that results in existing discrete handling math not coming into play? We do not reject a glass being slightly below a filling ring as being ripped off but would to being charged 10 percent more. Cents are modeled as a second variable instead of part of a whole for a variety of reasons. Brains tend to learn to skip "irrelevant" steps with experience. Thus we catch "shortcuts" like looking at only the dollar amount and not the trailing 99 cents. If we were dealing with say metal dust as currency we would be unimpressed by slightly smaller payment scoops as discounts.