It wouldn't be difficult at all to implement a collection of sales tax for each state that has sales tax (it isn't 50, by the way). It would be no more complicated that calculating the shipping cost. In fact it would be easier. The code linking the appropriate sales tax would simply be tied to the zip you enter on the billing address. Just a quick google search and I came up with taxrates.com
. I'm sure there are others. My guess is that private companies that keep track of this provide merchants with a way to keep up to date on the current tax rates for any area.
As for making sure the tax collected gets to the states, it wouldn't be hard for a company to keep track of the amount of quarterly sales to each zip. It wouldn't be hard for the IRS to verify the dollar amount collected and whether what is collected gets to the proper state's revenue departments.
All of that would be much simpler and quicker than the republicans in the House actually doing their goddamned jobs.