Re: @Tom No, this is bad, really bad.
Not so easy. Taxes have three or four tiers (federal, state, county/region, and usually municipal), and these tiers usually don't talk to each other. And even within each tier, taxes may be assessed differently for different things. Take Virginia. Each locality has a different tobacco tax on top of the state sales tax, then you get areas that charge an additional tax for hot-served food, there's confusion over whether or not energy drink count as grocery or merchandise (merchandise has twice the tax rate), and then there's the sales tax exemption for medicine and the tax holiday in August for school supplies. And all it takes to change these again is for a legislature to pass another Act or a city council to pass an Ordinance.
AND the federal government is notoriously inefficient. So do you still believe keeping track of such a complicated tax structure (which is necessarily complicated because the country is complicated) can be "trivially" done?