With the ban on cash transactions that you are talking about, it just raises stakes of getting caught.  But if the largest note was a 20 or 50, then it would be a whole lot more difficult to do these things off the books.  Unless you fancy carrying around a trunkload of the stuff. Presumably doing a transaction all in 20s would mean it would weigh 25 times as much as in 500s.

And I'll give my consent to any government that does not deny a man a living wage-Billy Bragg