The United States adopts the US Dollar. This system uses denominations of 1C (Penny), 5C (Nickel), 10C (Dime), 25C (Quarter) coins as well as notes in denominations of $1, $5, $10, $20, $50, $100 (referred to by their face value).
Money changing services can be found upon arrival at the Minneapolis International Airport, but are rare outside of the airport.
You can access Automated Teller Machines (ATMs) located everywhere (even in the most obscure bits) in Minneapolis, that accept most major credit cards such as Visa, MasterCard and American Express.
Finally, Major credit cards are widely accepted. Some smaller boutique shops may require an additional fee to pay by card or have a required minimum purchase amount, but most major retailers will not.