calculating sales tax

Unfortunately that option only applies to forms that use the product option(s).  My form includes selectable parameters (radio button) each with different values based on the customers choices, that shows a collective total at the bottom - then the customer submits taking them to the PayPal payment section.   I will post a link to form as soon as I have it posted on-line.

Yes. It is not possible to add taxes for custom payments/donations. In such a case you may need to calculate the taxes by using conditions wizard and adding few more fields to the JotForm. Please let us know if you need further assistance in this regard once you complete with building your JotForm. We will be happy to help.

Thanks!