This happened to me as well. I started off making $7.50/hour, then got bumped up to $7.72 after a few months. Turns out the people who were hired at the time I got my raise, started off at $8/hour. Once they got their raises, they were making $8.24! After a year I got a raise, and I was only making $8.19! There really wasnt much I could do about it, and I figured there was no point in making a fuss over 6 cents. Almost a year later I'm making $9.75 and about to get another raise in a month, while they're making less than $9, because I got promoted
I guess patience is the key!