There are a number of technical issues on the way of this as well. There are too many taxing jurisdictions. Here in PA the sales tax is 6%. But Allegheny County puts a piggyback 1% tax on making the total 7%. In some states the extra fractions of a percent are levied at an even more local, sub-atomic level. No online ordering system out there is capable of dealing with 10,000 localized sales tax rates.
That’s a good point. We have the same thing here in WA state, we don’t know what the sales tax will be from city to city and county to county without looking it up.