They are only countable if you give each a specific digit.
Person A: I paid $1,234.oo in taxes last month.
Person B: Which kinds of taxes did you pay for?
Person A: Let's see. Here's a list: Value-Added Taxes, Import Taxes, Witholding Taxes, State Taxes and Thumb Taxes. =P That's a total of 5 different taxes my money went into.
Damla, it's always hard when you get conflicting information. It's possible that in other places, taxes is always plural, and only in the U.S. do we use it in the singular, but I assure you that loophole is a countable noun all the time, and, in the U.S., at least, tax can be as well.