What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
Unfortunately sales tax is not built in to the payment too. If you're using paypal, you can setup a tax within your paypal account so it will be automatically added on your paypal checkout page when user submits the form.
Please check this guide
Also, another workaround is to create a separate product in your payment field and name it "Sales Tax", add a price and mark it as required by default so users will be obliged to pay. This would also be the case for shipping charges.