The unit of currency used in Indonesia is the rupiah (Rp). Coins of 50Rp, 100Rp, 200Rp, 500Rp and 1000Rp are in circulation. Notes come in 2000Rp, 5000Rp, 10,000Rp, 20,000Rp, 50,000Rp and 100,000Rp denominations. For change in amounts below 50Rp, expect to receive a few sweets.
Try to carry a fair amount of money in bills 20,000Rp and under as getting change for larger bills is often a problem.
By government decree, all businesses are required to price goods and services in Rupiah. Many tourist outfits such as hotels and dive shops try to price in dollars or euros to avoid currency fluctuations.
Tipping a set percentage is not expected in Indonesia, but if the service is good, you can leave 5000Rp or 10% or more (this is expected on Bali).