Is it on-topic to ask questions about money in politics?
Let's say, ask for an explanation about why x government asks you to pay some specific taxes, for example?
Or is it more on-topic in Politics Stack Exchange?
We've had well-received questions along those lines in the past. This one comes to mind:
However, as I said in a comment to that question, asking for the "why" in any tax law can be an exercise in futility, because the primary purpose of any tax is to generate revenue, and nothing is ever completely fair.
Politics.SE also tackles these types of questions, but at a more philosophical level, such as this one:
Another site that discusses taxation is Economics.SE. Here is an example:
If your question is about the specifics of a particular tax, I think it could work here. If, on the other hand, it is more philosophical, it would probably be better at either Politics.SE or Economics.SE.