As someone who hires people as part of my job, I have to agree with the above people. Indicate that are working, and have been working for more than a year. You can dress up the title if you like, to Retail Customer Service Representative, but don't be self-deprecating, with something like 'comic store flunkie'. If you want to keep it simple, just say 'Register Operator'. Mention responsibilities you may have been given, including closing out the register or locking up the store. Though it may seem menial, it means that your managers have imparted some degree of trust and faith in you. That carries weight on your resume.

I'm sure you have mentioned it already, but be sure to include the length of service with the CG. That also shows committment.