Green’s Dictionary of Slang

(US) an insignificant person.

1942		N. Algren Never Come Morning (1988) 118: He’d gotten down to the sprouts, the five-and-dimers, the penny-matchers [...] who’d never come closer to going on a job than to lean against the same newsstand that Bruno Lefty leaned on.
1973		Waylon Jennings ‘Old Five-and-Dimers (Like Me)’ 🎵 Too much ain’t enough for old five and dimers like me. / Mhm, mhm, an old five and dimer is all I intended to be.