As a software startup, how do you calculate sales tax in all the countries where your customers are?

And then, how do you pay sales tax to governments of all of those countries?

My question comes from the fact that on our website, customers can sign up from any country. Calculating and paying tax in an unknown number of different countries seems to be more complicated than building our product.

*specifically asking about sales tax + new 'digital' taxes. How do you deal with that?