Green’s Dictionary of Slang

dimmo n.1

also dimo
[SAmE dime + -o sfx (1)]

(US) a dime, ten cents.

[US] Wash. Post 28 Mar. n.p.: The word comes from the slang of the street arab, who has a name for every coin. A ‘meg’ is a cent, a ‘jit’ or ‘jitney’ is a nickel, a ‘dimmo’ is a dime, and a ‘cute’ is a quarter.
[US]Wentworth & Flexner DAS.