If you've been asked to pay a tax at checkout, then it means that we are required to report sales taxes in your state/country. Every state has different requirements and thresholds for collecting sales taxes (these requirements are called "nexus"). Sometimes you will even see county and city taxes.
Many businesses (especially small press publishers selling online) don't understand how to charge or report sales taxes correctly, or don't have the volume in a state to cross the threshold for a nexus there. Others pay taxes from their own receipts and just don't expose this cost to backers. So there are a lot of reasons you might not have encountered this before. It doesn't necessarily mean that other creators are doing business correctly or incorrectly.
If you are a tax accounting professional and you believe that sales taxes are being calculated incorrectly, please let us know. We will escalate your concerns to Shopify, who manage the tax collection algorithm.