Proper Taxi Driver tip?

[Traelin]

I'm going to Chicago in February and I'm hearing conflicting reports on what is a decent tip for a taxi driver? I'm going to be taking a taxi from O'hare to my hotel between Michigan Ave. and the navy pier. I expect it to be around $50 as it was last time. Any suggestions or advice?

[Taernath]

$5, less if he talks to you.

[Kitsun]

10% is fair. If he helps with luggage, is friendly, or gets the hint if you just want to sit and stare, punctual, doesn't drive like a maniac, etc you can go up to 15-20%.