In all honesty, yes you should be charging more. Not everyone can create banners that a) look good... b) catch the viewers eye... and c) make them wanna click.
I mean ... I don't know much about your work but it generally seems quite good ... $10 ... I mean ... seriously, over here, McDonalds pay more per hour and I think you should be charging based on the fact that you're a creative skilled person. You're charging for your time... but you should charge for your skill too ...
