For a cashier, you are hiring someone to essentially be the "face" of your business. I dont think anyone in their right mind would want someone that looks like they fell face-first into a tackle box representing them.
Its your business, so its your choice. I wouldnt consider it discrimination. If someone gets hurt and has limited movement, thats not their fault. Skin color, injuries, religious viewpoints- should all be grounds for discrimination. Using your face to test Rapala tackle is a choice, and should be treated as such by everyone.
An aquaintance of mine from a previous job works for the company that cleans and waxes the floors at my present job. He has bolts thru his nose, a safety pin in his eyebrow, tattoos all over his arms, and those stretched out tribesman ear-lobes freaks are running around with these days. Every time I see him, he complains about not being able to find a job. I wonder why.
I never had much use for piercing. I figured I spend too much time trying to keep from poking holes in myself, to turn around and pay someone to do it for me.