something is not working out in this explanation:
1. First of all a bit about taxes in the USA. The USA simply does not have VAT - so nothing to include, but it is what you supposed I believe, that is OK. Instead they do have common 'state sales taxes' state-wide, and more local surtaxes, which may be defined by county. There is no US state with higher than 7.5% local sales tax, or higher than 12% average tax including local taxes. Which makes the worst possible price (if not point 2) for US - 55$, exactly same cost as for EU, so definitely no one going to pay any "differences" that you mentioned.
2. I have just registered via proxy from Louisiana, which is according to https://www.usatoday.com/story/money/taxes/2018/03/27/states-highest-and-lowest-sales-taxes/452512002/ has the most avg tax in the USA, and I am able to buy pack for 49$
So apparently there are no sales taxes collected from online payments. I am not going to investigate per-state requirement to collect online retail tax, but as we can see from simple experiment - you can easily buy game for stated 49$ in US (after processing to paypal - it still shows 49.99$ in the final checkout).
4. I still can buy pack from retailer from Austria for 49$. https://store.markeedragon.com/catalog/Crowfall_Patron_Backer_Pack.html