[quote=@MMGiru]
Also, is it weird that all these countries at war so often use the same currency? I was wondering if it's minted in Tetsu no Kuni, or something, given their neutrality.
[/quote]

That's quite an interesting point, and I do believe you might be on to something. Tetsu no kuni (land of iron) and their samurai have acted as keepers of balance and peace for a while, and it would not be strange in any way if they were also the minters and printers (I will butcher this language if I want to) of the standardised currency.

However, a side note. 
In Scandinavia, the cold bloody hell up north that no one really cares about, there are two countries that exists side by side. The interesting thing is that they also share the name of their currencies, crowns. While they don't have the same value, the currencies are named the same, and as long as you are close to the border they are practically interchangeable. Perhaps something similar is at work in Narutoland?