Most tourist-oriented businesses quote prices in dollars, as do most grocery stores in the larger cities. Small stores may quote prices in riel, but they will all accept dollars as payment. Unlike in many countries, if you pay in US dollars the exchange rate you will get is quite fair. At the time of writing the official exchange rate is 4,002 riel to the dollar, versus the street rate of 4,000 to the dollar, a difference of less than 1 cent.
Because they don’t use American coins in Cambodia, you’ll get change for your purchases in riel (1,000 riel is 25 cents). If you do want to change money so that you have riel on hand, you can do so at any bank in Cambodia. You’ll get better rates in the local markets, where you’ll be able to identify the moneychangers by their glass cases filled with piles of notes. Be warned, though, that it’s rare to find notes over 10,000 or 20,000 riel ($2.50 and $5, respectively), so changing a relatively small amount of US dollars can leave you with a big pile of cash.
At border towns, such as Koh Kong or Ha Tien, you’ll often find the currency of the neighboring country also in use, meaning there can be three currencies in circulation: the riel, the dollar, and the Thai baht or the Vietnamese dong. If you go through a land border, you may be told that there are no ATMs in the next town, or that you need Cambodian riel to get through. This is not true, and visa prices are charged in US dollars.
In the Cambodian countryside the economy is almost entirely in riel, but even so you will always be able to use dollars in small denominations. Do not expect anyone to change a $20 bill for a $0.50 purchase, though, so plan ahead and have lots of $1 and $5 bills. Your US dollars will be rejected if they are ripped, torn, or otherwise overly abused (although you can expect to see filthy riel in circulation). Old-style US bills are also not welcome, so make sure that the cash you bring is fairly new.
ATM machines in Cambodia dispense US dollars and Cambodian riel. However, if you are using a foreign ATM card, you will only be able to withdraw dollars.
ATMs are widely available, including in all major tourist centres and provincial capitals. Credit cards are accepted by many hotels and restaurants in larger cities.
Tipping is not traditionally expected, but in a country as poor as Cambodia, tips can go a long way.
Hotels Not expected outside the fanciest hotels, but 1000r per bag plus a small tip for the cleaner will be a nice surprise.
Restaurants A couple of thousand riel at local restaurants will suffice; at fancier restaurants you might leave 10% on a small bill, 5% on a big bill.
Remorks & Moto Drivers Not expected for short trips, but leave a dollar or two for half-day or full-day rentals if the service was noteworthy.
Temples Most wats have contribution boxes – drop a couple of thousand riel in at the end of a visit, especially if a monk has shown you around.
Service Charges Many of the upmarket hotels levy a 10% service charge, but this doesn’t always make it to the staff.