You are surely right about the translation five bucks. I don’t in French quebecois, but in French, from France, the equivalent expression in slang would be cinq balles.

I don’t know Quebecois French but I have found this post on Projet Babel confirming the use of pièce as slang for money in Quebec:

Ici au Québec on dit des pièces (pas très original), et certaines personnes disent des bidous.

There is an incredible number of slang words for money in French (I suppose it must be the case in most languages). On that page on Projet Babel you will probably find most of them, even those used in Belgium and Switzerland. And for some of them they give the origin of the term.

In France I expect thune is probably the most common. Une thune originally was slang for a 5 franc coin (when we still had francs), but it has come to be used as a generic slang word for money, file moi de la thune¹, t’as pas de la thune?² are probably common phrases among French young people. Blé, oseille, pognon are also quite common and used as also as generic terms for money in slang.

Balle which was originally used for a franc, is sometimes still used with euros but it can only be used with a numeral in front of it.

¹ “gimme some dough”
² “got any dough?”

I am from Quebec. You are mishearing the characters. They are not saying “cinq pièces” but “cinq piasses“. A piasse is a mispronunciation of “piastre“, which derives from the Italian piastra, meaning “thin metal plate”. The term was applied to currency pieces of the 16th century and the term started being used in New France. Over the years, the final -tre got left out of the pronunciation. It’s a colloquial way to designate a dollar.

There are other slang terms referring to money as Laure says, but in Quebec, piasse is definitely the predominant one.

@Kareen’s answer is correct. I’m also from Quebec and what you’re hearing is "piasse", which as was mentioned, is very predominantly used.

The geopolitical nature of Quebec has given its spoken French a wealth of words borrowed from English, sometimes Frenchicized, other times just used as-is and merged into the sentence: it’s not rare that money is referred to as "du cash", as in "[t’]as-tu du cash?" (got money?) or "awaye, le cash!" (the money, quick!)¹.

When talking petty amounts (except irony, of course), you’ll also hear "change" (French pronunciation) for pocket change.

_{¹You probably heard that one already in some Kwik-e-Mart scene 😉}