I just realized that: If you have taxes with decimals (like 2.5 %) – all the calculations will be fine – however, it will only show that you have 2% taxes. You might want to include this minor issue in the next update.
I figured it out by myself: In the Localization Settings there was taxes defined with “Taxes: %d%%”. However, since d is an integer, it will cut off all the numbers after the point. So I changed it to “Taxes: %.1f%%” and it works like a charm!