"Quid" and "guinea" are both slang/informal names for "pound," right? Much as a "buck" means a "dollar" here in the US.

In the US, a "fin" is a $5 bill. I intended to also provide the corresponding old-time slang name for a $10, but am having a brain-fart at the moment.

A $100 bill is a "c-note" (for obvious Roman-numeral reasons, not anythning to do with music) or a "benjamin" (because it displays a portrait of Mr Franklin).