Adding tax to the payment form

How do I get a tax calculation to be based on my State base plus the individual City's tax ?

Unfortunately inside of payment tool it is only possible to add one tax option e.g. for States.

Inside of this article you can find out how to add tax to your Payment Form:

http://www.jotform.com/help/296-How-to-Add-Tax-to-Your-Payment-Form 

Hope this will help. Let us know if you need further assistance.