tipping on shared ride services

This may be a dumb question, but are you supposed to tip the drivers of a shared ride service such as Tri County?

[CA Cruiser]

I feel that if they help with your luggage and take you to your destination timely a tip is in order. We usually tip $1 bag and per person. I have seen others just give a flat fee like $5.

[Donna]

Yes, I'd also tip a dollar or two per bag.