[jandrewrogers]

It depends on the locale but usually not more frequently than once per quarter. Aside from this, one aspect that makes it complicated and intractable is that the rules for applying sales tax to various goods sometimes require very late binding -- the correct tax rate cannot be known until checkout because it is dependent on customer decisions at checkout. The common example of this is the definition of "prepared foods", because something you are going to eat immediately gets taxed differently than something you are going to take home. Tax authorities have standards of evidence at checkout based on customer behavior for food items that could reasonably fall into either category.

An argument could be made that sales tax should have rules that don't require this type of very late binding. The issue is that legal authority over this is completely decentralized as a Constitutional matter and there are thousands of overlapping tax authorities. There is no feasible way to compel them to all do something sensible, so the system has to operate under the assumption that some tax authorities will issue these types of rules as a matter of robustness.