Note: No matter what you name your dollars, you cannot change the value. If you rename it Bananas, it is still worth $1 USD. Keep this in mind as it can create frustration with employees if you rename it something that doesn't make sense (like naming it after a different country's currency - British Pounds for example) Transparency around the dollar is part of the Motivosity magic. If you change it, we warned you!
Note 2 :) IF you have employees in another country, they will be shown a conversion to their local currency automatically. This means if they have $50 for example, they will see something like [Your current balance] = 40.14 GBP on their home page and in the store if they were in England.
In the Preferences part of your Setup tab, you have the ability to change the currency symbol and nickname. The default is seen below.