Is there an exact reason why is 10% of your profit taken? Does it go somewhere, or is it just kind of like an addition to make in-game marketing more realistic?

Honestly, good point. I don't know. They just disappear from your profit. I think it's to make marketing "realistic". But I feel like it's pointless if these taxes aren't actually used up. For example, in real life a government would use up it's people's taxes to work on the community.