“Do you want that all in ones?”

A customer at your part-time job asks you for change for a $20 bill. You want to know if they need 20 one-dollar bills, two ten-dollar bills, four five-dollar bills, or some other combination. You ask:

Do you want that all in ones?

(an amount of money) in (a denomination)

Different types of bills (one-dollar bills, 100-dollar bills, etc.) are called "denominations". A very formal way to ask the question above is:

In what denomination would you like your change?

You use the word "in" to express the denomination of an amount of money:

Can I get that in twenties?

Drug dealers in movies always carry briefcases with thousands of dollars in hundred-dollar bills.

ones

In the example above, "ones" means "one-dollar bills". Whenever you're talking about money, holding your wallet, paying a bill, etc. you can just use the word "ones" to refer to one-dollar bills.

For other types of bills, the names are:

fives

tens

twenties

hundreds

I'm not really sure what the denominations of bills in other contries are called.