Sales tax and VAT are different
US sales tax is added at checkout on top of the displayed price, and the rate depends on the state and often the city or county. VAT is built into consumer prices in most other countries, and the displayed price already includes it. That is why the two calculators work in slightly different ways, although the arithmetic behind both is the same.
Pricing for different markets
If you sell in several countries, work out the price your customer sees, then remove the tax to find what you keep. Use the net profit calculator or the platform fee calculators on the tax-free figure. These tools do arithmetic and are not tax advice, so check your obligations with a tax professional.