Family Dollar

Came to thus store a few months ago like 9am.. so I had 2 $20 dollar bills. I purchased something then I ask for change with the other $20 she said she didn't have it ( now ik thinking some tell you that cause they think you will Rob them or something, so I guess if I purchased something I would get the change , the So called Manager Denise got a attitude. . And that's really ticked me off! But the other customers got there change from a $20.. Another time I went there a Caucasian lady in front of me gave the cashier a $20 bill he didn't used the marker to check it when I gave him mines he looked at it in the light and used the pen and he was African American also...