Tax Categories will usually have been set up in development and will rarely change. If you do need to change them, go to Administration > Tax Category.
You can download documents with domestic and international tax category information via this screen. Simply click on the appropriate hyperlinks at the top of the screen. For full information, see the iAPPS Developer Documentation.
The out-of-the-box Sales Tax calculations for iAPPS Commerce comes from tables using US zip codes, which occasionally fall in more than one tax jurisdiction. Tax Tables are updated with each iAPPS release. International tax information requires an account with CyberSource.