Race Trac Simple Lame $5.00 Rip Off Benbrook Texas

I come in and buy 3 packs of Marlboro Special Blend a couple times per week. I always pay with a $20.00 bill. The cost is $15.39, sometimes I have the change, sometimes not. Sunday morning I made my purchase, gave the coins of $0.40 and a twenty dollar bill, said keep the penny. In a bit of an early morning fog, I started walking out without the $5.00 change. I barely got out the door and came back, there were no other customers that had transacted anything. I ask for my $5.00 change and was told I paid with $16.00 and the cashier produced some receipt that said I did. Now, I'm not stupid, senile, slow or dim-witted. I left my home that morning with 2, $20.00 bills. I paid for the cigarettes with one of them, period then end. Now when I ask for my change the two people there stating putting money in the safe, from the drawer, while the other started counting, and of course...their drawer was "right on." I've been ripped off for $5.00. It's just stupid the way they handled it all.