During the medieval period there was no currency used throughout the whole of Germany. Most used the Silver Penny (Pfennig) but there were different types with a different value (amount of silver in them) that also changed over time (some were more stable, some changed every year). People were obligated to exchange old coins for the new ones and part of the exchange was held back by the people in charge (the so called Schlagschatz). Also people coming from a different location were obligated to exchange their coins or silver bars to the local currency at the time. The exchange rates were quite different.

It was a complete mess. But somehow it worked.