[msla]

> I would argue that financial math by definition needs to be accurate to the penny. Where is "pretty close" financial calculations considered acceptable?

Computing tips, from the standpoint of a customer paying the tip.

Saying "pay 20%" isn't precise to begin with, in that you will not use fractional cents to make it precise, so having a tipping granularity a bit larger than a penny is also acceptable, particularly in jurisdictions where there is no one-cent coin (or equivalent) in any event.