The CNMI uses the US dollar exclusively. The islands are fairly expensive due to their remote location, comparative wealth and the profusion of free-spending Japanese and Korean package tourists, so figure on at least $100 a day for travel in any comfort this being also the entry requirement. As the CNMI receives most of its visitors from countries where tipping isn't customary, restaurants do not expect tips but will be happy to receive them anyway.
Major credit cards are accepted at most retailers and restaurants. On Saipan, the major banks, and some restaurants and stores all have ATM machines. Bank of Guam has branches on Tinian and Rota, complete with ATMs.