In Japanese money is okane (お金). The currency used in Japan is yen. In Japanese it's pronounced en (円). For countries that use the dollar as currency, below is general rounded up/down estimate as to what yen is equal to.
1 en = 1 cent
100 en = $1
1000 en = $10
When you are in Japan and speaking Japanese it's important not to use the English pronunciation of the numbers, they are not used in Japanese currency. When you count currency it's the same as the regular numbers.
800円 = happyaku en
3000円 = sanzen en
2400円 = nisen yonhyaku en
When numbers reach 10000 ($100) they are counted in groups of ten thousand, which is man (万). The extra zeros are also not usually written.
1万円 (10000円) = ichiman en
22万円 (220000円) = nijuu niman en
43万円 (430000円) = yonjuu sanman en
A lot of English speakers like to think of it as counting in groups of hundreds when they get to larger numbers. This is because 1万 is almost equal to the amount of $100. 15万 is similar to $1500 (fifteen hundred).
Japanese numbers takes some getting used to, but thankfully most registers in Japan have a digital screen that will show you how much you need to pay.
The polite form of suru is also used to express how much an item will cost.
This costs 5000 yen = kore wa gosen en shimasu
It costs $4 = yon doru shimasu (4ドルします)
That car costs $4 = ano kuruma wa yonsen yuuro shimasu
How much is it = ikura desu ka (いくらですか)
Coins & bills
In Japan most people use cash (genkin 現金) to pay for items, rather than a debit card. Below are the current coins and their values that are used in Japan.
Coin = koin (コイン)
Bill = osatsu (お札)
There are 4 types of bills that exist in Japan. 1000円, 2000円, 5000円, 10000円. 2000円 bills are rare in Japan because they were only produced to commemorate the G8 summit in Okinawa, and the millennium year. Most vending machines won't accept them, and even some stores do not accept them anymore.
In Japan it is very common to see a small tray at each cash register that is for putting your money in it to pay for an item. Instead of handing your cash directly to the clerk, you put it in the tray. Most of the time the clerk will hand you your change directly, but sometimes they will put it into the same tray for you to take yourself.