I think that’s also because a couple hundred years ago practically every currency was just a certain weight of gold, silver or copper. Different coins were just an easy way to recognize the weight.

Maybe we need to get some numismatics to weigh in here, but I think currency could be extremely tricky depending on where and when you were. I remember reading about medieval Italy and it seemed every city issued its own currency with different denominations, names, and weights. And even then, people would be scraping them to get some precious metals off of them, and with all those different currencies, counterfeiting must have been a real issue.

To apply this Tolkien, the Shire would probably have a different currency than even Bree, though Butterman would even take your coins from Gondor out of politeness to travelers.