Much of Lake Superior's currency is based on copper, which is locally plentiful and has many practical uses. The elves of Isle Royale use their own currency, the markka, which converts to 100 penni.
1 platinum piece is equivalent to 10 gold pieces is equivalent to 100 silver pieces is equivalent to 1000cp.
The currency of Tammisaari is the Markka, an electrum disk struck with the face of the current King of Tammisaari on the obverse (Pikko Vainola), and beautiful birch tree on the reverse. In the town, depending on current economic conditions, the Markka trades for 120-190cp (d8 x10 + 110).
Each Markka is worth 100 copper penni; penni typically trade 1:2 penni:copper.