The problem in the US is that the local sales tax is the sum of sales taxes created by several independent authorities. These authorities have varying geographic and subject matter scope, and can modify their sales tax on their own schedule. There are effectively thousands of independent sales tax jurisdictions in the US and the details of the computation in those jurisdictions churn regularly. By “late binding” the sales tax, they avoid having to churn the printed/published prices.
I think there is also a policy view that taxes should not be hidden, that there is a public interest in making the public aware of precisely how much they are paying in taxes. Taxes that are baked into the price tend to be forgotten about by the public.
