The local tax is set by multiple independent tax authorities that change their taxes independently, the tax you see is the aggregate of those independent authorities computed separately, which do not coordinate with each other.

Some of these taxes are conditional at point-of-sale, late-binding the taxes, such that different customers are subject to different rates across these tax authorities such that it is unlikely to round to exactly 5c.

It is widely illegal to not display the true price and taxes paid separately. Trying to retcon a price and taxes for rounding purposes that is also strictly consistent across customers so as to not violate the law is not trivial.

And on top of all of this, the Federal government does not have the authority to regulate the way States and various locales structure their sales taxes. It is a herding cats problem.