Another thing that few (if any) games address is, depending on time and location, medieval Europe wasn't fully a cash economy. If you roll into a sleepy village, being able to buy and sell in money may not be possible, regardless of what coins we're talking about.
Even as late as the composition of Domesday, some tenants in England were paying their taxes in kind, rather than in cash or in service.
That made William a bit unhappy, as he wanted to use England as a tax farm to fund his wars in France.
That's what led him to induce Jewish moneylenders from the continent to move to England: people who had paid tax in sacks of grain or whatever then had to borrow money to pay their dues.