The Punt/Pound example mentioned above is spurious, the change given (in my experience - although initially I had doubts until the system was explained)) reflects the official exchange rate between the two currencies, and all transactions across the border were approximately equal.
But a situation existed (and may still do) in England where although the Scottish and English pounds had equal official value, English shopkeepers would only give 19s 6d value for a Scottish pound note, despite getting £1 value when deposited in their bank. In this case it is easy to see that the extra 6d comes from the pocket of the customer offering the Scottish note, as they do not receive full value for their money.
In the example, the dollar has the same value in each currency, so the innkeepers make no loss exchanging notes, again the loss is borne by whichever customers spend currency from the other country.