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"In universe" I think it makes sense that coins would come in different denominations as well as different materials. Their value isn't just in the physical metal that makes them up, but the listed amount (which would be backed by whatever government or group minted them)
For my players, I actually hand out coins (campaign coins) in copper, silver, gold and platinum along with semi-precious "gems" and prop jewelry. The coins come in different denominations (a 1gp coin, a 5gp coin, a 10gp coin, etc) to make it easier to manage large amounts of currency.
Although it isn't officially a pathfinder rule, I recall reading in one of the old D&D edition books that standard gold coins weren't actually made of solid gold, but more likely gold plated or alloyed. I also recall reading in an old magazine interview with Gary Gygax that one of the reasons he added copper coins was to give players a giant dragon horde of them such that they couldn’t possibly truck them all out of the dungeon as a bit of a joke. When they came back for another load of treasure they found that other monsters had moved the remaining loot down to the next level, resulting in a player/DM arm’s race where players would drag in donkeys and hirelings into dungeons to remove their coins before other monsters could claim it.
To wrap it up, if you are looking for additional complexity and realism, making players bank money, or using things like gems to carry larger amounts at a time would probably work out well. Or you could just give them mountains of copper and see how they fare…