Green’s Dictionary of Slang

(US) a 25-cent coin (rather than the equivalent sum in smaller change); thus case dime on same principle.

1940		Courier-Post (Camden, NJ) 9 May 32/4: Spectators [...] learned a ‘case quarter’ was one in a single piece, that is not divided into different coins.
1956		N.Y. Age 22 Dec. 4/2: ‘I didn’t have a case quarter [...] to buy him a present’.
1973		Atlanta Constitution (GA) 9 May 4/5: I asked about a ‘case dime’. FlynnWarren [...] tells me, ‘The term “case” is used to describe the quantitty of money held in a single piece of coinage. Thus two nickels (10 cents) are held in one “case” (the dime). Thus, two dimes and a nickel would make up a “case quarter”’.
1989		H. Pekar American Splendor 11 [comic strip] Hey, Harvey, you gotta case quarter for two dimes anna nickel?
1992		Phila. Dly News (PA) 14 Oct. 8: [photo caption] A case quarter can’t buy much.
2017		Times & Democrat (Orangeburg, SC) 19 Mar. A4/4: Several guardian angel coins lie among pennies, dimes and a case quarter or two .