The local currency
Local currency is Argentinean Peso which is used throughout country. However, there are some stores/shops where you can use American Dollars.

Euro is another currency accepted and it can be exchange in local Exchange Houses in San Miguel de Tucumán.
Where to exchange money
You can exchange your money on the bank area, located at downtown in San Miguel de Tucumán. Most of them are at 700 San Martín Street.
Means of payments enabled on the Province
Even though cash is the most convenient, there are lots of stores/shops, restaurants, among others where national or international credit or debit cards are accepted.
Tips are not compulsory. It is up to each person to give the amount of money they want to the people who offer different services, such as, waiters in bars and restaurants or the people who may help you with your luggage at the Bus station.