If you need to change money, there’s a Raiffeisen bank with an ATM among other banks, in Jugoslávská street, that’s the street at the lower end of námestí Míru square down to metro C line stop I.P. Pavlová (Which connects you with both the main railway station, Hlavní nádraží, as well as with bus terminal ÚAN Florenc).
There is also a bank with an ATM in Vršovické náměstí 67/8, that’s a short walk down Donská street. Turn left at the next corner down Charkovská street till you bump into Krymská street, turn right and walk down a 160 m to a subsidiary of Česká spořitelná bank.
Rather abstain from changing at private exchange offices; some of them offer very disadvantageous exchange rates. It is not recommended to pay in € at restaurants and shops either, unless they publish their exchange rates.
The local currency is Czech Crowns, CZK. The Czech Republic is not a member of the Euro countries.
For easy conversion:
1 € and 1 US $ are approx. CZK 25 (September 2015). See precise exchange rates HERE.
Coins: CZK 1, 2, 5, 10, 20 and 50, banknotes: CZK 100, 200, 500, 1,000 and 2,000.
1) Ticket machines usually don’t accept coins of CZK 50 (The one on the bottom, right)
2) ATMs deliver sums in steps of CZK 200, e.g. CZK 400, 600 or 1,200 etc.
If you punch in a sum of CZK 1,000, you get a KC 1,000 banknote, which is not very useful for small shopping; rather request CZK 800 or 1,200 etc.