Great question! Thanks for the discussion. I've found similar charts, and initially figured I could use those as well. I mean, how hard can this be right?
To be honest, your source for the zip code info seems a little sketchy. How do you know it's accurate? What is the original source? Clearly though, the Florida DOR is the definitive source for tax info.
The crude maps I produced used US Census Zip Code Tabulation Area data. ZCTA's are perhaps the best "mapped" approximation of zip codes you can find for free.
Try this: go to zillow.com, and do a search on zip code 32640. It's hard to see, but you'll notice a very faint line that splits that zip into two pieces... one in Putnam County, the other in Alachua County. Maybe by dumb luck those two counties charge the same for sales tax, in which case you'd be fine. But what if they don't?
If you really want your head to pop, read this: http://en.wikipedia.org/wiki/ZIP_code
... thus, zips may seem fine at first glance, but when you dig in, it may not be so.
I really wish I knew how the big online merchants with brink and mortar stores figure all of this out! Probably big $$ to throw at commercial services.
Thanks again.