There are two ways it can be done:
1) charge the local rate where the seller is located.
2) charge the local rate where the buyer is located.
If 1), the buyer is being taxed by a jurisdiction where he has no vote .... that is taxation without representation.
However, this is workable, and is really no different than when buyers voluntarily cross jurisdiction lines to make a purchase.
If 2), (which no doubt will be the case) there are thousands of jurisdictions, as John points out above. I suppose someone will create a software program to convert zip codes to tax rates. Such software will require updates on an annual basis, which will entail added costs to the retailer.
However, the cost and complexity I note above, is the least of the retailer's nightmare. When the retailer submits his sales tax return, he must allocate the precise dollar amount he sold in each of the the state's counties, and sometimes in the particular city as well. This is not a supposition .... I now fill out such returns, on a monthly basis for some states. This is workable for me since my sales locations are singular in the various states. Imagine the complexity if the sales locations become the buyer's address.
Needless to say, the cost to the buyer will increase much more than by the tax rate.
I am sure many retailers will quit on-line sales, or drop ship using a third party such as Amazon ..... another case of the rich getting richer. Of course, Amazon supports taxing the internet.
Slick