hey scrappy, I randomly went through I guess you would say "normal sized keys". Looking at my notepad I used letters a,l,b, numpad 2 and 4, enter and lastly the up arrow (the one not on the numpad) was also used.
I made sure to set the nickles down slowly, which was more difficult then I thought because my hand was shaky lol. Also made sure to play with putting a stack with minus one nickel to see if it would register; if I was careful in the case of -1 it would depress but would not register it in notepad. Space bar was consistent with 14 nickels placed directly in the center.