Yes the one state/one tax rate example I gave was strictly for a demo. You would have to create FL, then upload the csv file from taxrate.com that has it broken down by zip code, and do that for every single state. Quite the pain in the butt, but will work. I'd love to see your plugin. Can you email it to me?
We have a couple people beta testing the US product. Please feel free to contact via the link in one of my posts above for the world-wide product (though the Dokan now has a nice tax capability built into it that may suffice for most people world wide just not US). If you have a marketplace you've launched (or in testing with products, etc) we can work you in as a beta tester. The software will be available soon (to all) though.