Q:

What does "a nickel" mean?

From the Dark Knight movie (2008):
A criminal called Joker comes to the Mob Bosses he's stolen from earlier. They're obviously mad at him and he adds more fuel to the fire saying that they're gonna lose all their money if the Batman doesn't die. 

If we don't deal with this now, soon little Gambol here won't be
  able to get a nickel for his grandma

After that Gambol flies into a tantrum and tries to kill the Joker.
I wondered if "a nickel" meant 5 cents or could it mean something like "a bag of drugs".
There's no other context I can give. We don't know if Gambol's grandmother is junky or if he's been giving her 5 cents per day. 
I' wondering if it's possible to say exact definition of "a nickel" in the context. 

A:

A nickel here has its ordinary sense, a 5¢ piece. 
The Joker's line here depends on familiarity with the common similitude that "X is so greedy/crass/inhuman that he would sell his grandmother for a buck" (or some other low price). The Joker implies that Gambol is just such a person, but that conditions will decline to the point when Gambol won't be able to get even a nickel—crime won't pay any more, and the most despicable deals won't yield any profit.

