Green’s Dictionary of Slang

(drugs) $5 worth of drugs, the quantity varies as to the drug, more marijuana, less heroin.

1966		J. Mills Panic in Needle Park (1971) 20: Often the junkie pusher will deal ‘nickel bags’ at $5 each, as well as $3 ‘treys’.
1975		E. Torres Carlito’s Way 24: We was small-timing in them days — thievery, nickel bags and strong arm.
1981		H. Gould Fort Apache, The Bronx 32: He could move right in now on the dude [...] and probably collar him with cash, five nickel bags of dope.
1993		R. Shell Iced 14: I walked into Washington Square Park, bought a nickel bag.
2000		M. Collins Keepers of Truth 70: A pipe and a nickel bag of pot.
2010		(con. 1973) C. Stella Johnny Porno 31: Some young kid from the neighborhood looking to deal nickel bags.
2017		D. Winslow The Force [ebook] [T]hat community who’ll rob each other, cheat each other and kill each other for a nickel bag.