The local currency of Indonesia is Rupiah. Bills come in denominations of Rp 1000, 2000, 5000, 10,000, 20,000, 50,000 and 100,000. Coins come in denominations of Rp 100, 200, 500 and 1000. At the time of writing exchange rate is 10 000 IDR = 0, 87 US$ and 10 000 IDR = 0, 68 EURO (October 2014).

In addition to the local currency, both Singapore and US dollars are readily accepted in many places and most mid-range hotels, all top-end hotels and restaurants list their prices in US dollar.
Exchanging money, either banknotes or travellers cheques, is easy at banks and authorised moneychangers in major tourist destinations, and credit cards are accepted at most hotels and restaurants in main cities, but can present problems elsewhere, so it’s best to ensure adequate cash before setting off to more remote locations.
Banking hours are generally from 8 a.m. to 2 p.m. Monday to Friday and until 11 a.m. on Saturdays, but exchange rates offered by the moneychangers are generally better than the banks, they stay open longer and transactions are quicker.

ATM’s are easy to find in the major regional cities and tourism areas in Indonesia with many allowing cash withdrawals from debit cards. Most of them are connected to international banking networks, thus making it possible to look for machines that are affiliated with your own ATM network. Although credit cards are accepted in many places, credit card fraud is a significant problem with “card cloning” on the increase.
Also don't forget that there is a Rp 150,000 departure tax payable only in Rupiahs at the airport upon departure. So please keep this amount aside on the last days of your stay in order to save time running around the airport to change the money.