B/X Known World
I used taxes as a joke once. The players immediately started scheming how to avoid them. Bury the loot outside of town. Bribe the tax collector. Hire bandits to rob the party at the edge of town so the townsfolk could see them get robbed. It led to way more cool quests and shenanigans that I expected.Know what can make D&D more realistic? Taxes! Nothing will immerse your character more then calculating how much of your loot is taxable!