G.B.
I'll answer this from the point of being a boss.
I was never comfortable with the fact that people who worked for me bought me gifts. In fact, I asked them NOT to. As one mom said, it is not a personal relationship, it is supervisor/subordinate.
I think that unless you are VERY close to the boss,(which is usually not a good idea either) you would be wise to go along with the group gift, just put in a couple of bucks.. and move on. The fact that you guys are buying something for the boss at all, is a gesture that is above and beyond. Buying something on the side might look like you are trying to get in good with him/her.
I would throw in $3.oo and spend the 20 bucks on my husband or child.