IMO you can do whatever you want as a finale.
You can pitch the finale to keep the crowd around you, and stay long enough to collect hat. the few times I did a busking show, I pitched a feat that involves a prize, and a contest of strength. If you think you can tie me down to this chair, using 100 feet of rope; And keep me from escaping, in the same amount of time that it takes you to tie me up. Pleas stay until the end of the show. I kept the pitch going in between different, effects and routines. At some point I revealed if they are successful in tieing me down, and preventing me from escape; the participants would each get 100 hundred dollars.
Now I do not suggest you go to Penguinmagic forums, themagiccafe, theory11, or any other mainstream magic forum. I suggest you go to google and luck up "busker forum" "busker community" in the search bar. You will fain access to the best information out there in the way of busking.