Counterfeit Fives are out there. I just saw one yesterday - an awful color copy which looked like someone pissed on the bill.
I remember back in the early 70’s copying a dollar bill on a black & white copier. I was surprised how good it looked, even without color, of course if anyone was at all being careful they would spot it as a fake.
With modern copying equipment it should be easy to make halfway decent copies.
BTW, I was just looking at some old German money by father brought back from WWII. It was actually made in the early 1920’s and was way better made for defying copying than our current money. It had all kinds of interesting colors and watermarks.