a penny saved is a penny earned

i've never been a monetary genius.
i work, earn money, spend some and save some. i don't buy much on credit and pay all my bills on time. i would imagine i'm in the same category as many people when it comes to my money handling skills, only possibly slightly more on the conservative side.
but living here in miami, i've begun to notice something that i don't recall noticing before. it has been about 18 months since i came to reside in the magic city, and starting about 3 months ago, i noticed that not every cashier gives me back my correct change.
example:
place: taco bell
items: cheesy bean and rice burrito and a crunchwrap supreme
total cost: $2.99
paid: $10.00
change owed: $7.01
*here's the kicker*
change received: $7.00
a discrepancy of one cent.
normally, being shorted a penny wouldn't bother me. people make mistakes, , a nickel is mistaken for a penny, incorrect change is handed out, yadda yadda yadda...
but the problem is that it has happened at least four times recently. maybe i wouldn't have ever noticed it if i hadn't had gotten off on the wrong foot with a cashier at the local snack shop at my university. she owed me a penny after i bought some chips, and as i was there waiting for her to give me my receipt and penny, she looked at me with a snide look and said, "do you really want your penny?"
"yes, of course" i calmly replied.
she looked at me as if i had lived in some parallel universe where i had missed the memo that actually wanting the change that was rightly owed to me was some sort of prerequisite for hospitalization.
then a couple of days later it happened again. i was in a local pharmacy getting some supplies when i just happened to have one cent over my total. i handed over the money and was given in return only my reciept. no penny...
second time same as first, only this time no option.
the third and fourth times were at local eating establishments where, in the same way as before, i gave exactly one cent over my total and was given nothing in return. i had the full intention of putting the penny in the ronald mcdonald fund, but even that chance of a small contribution was denied to me.
why all the fuss over four cents? i've thought of at least two lessons i've learned...
1) no matter what the value, one must be respectful of others' belongings. give people what they are owed, in the name of integrity and fairness. faithfulness in the little things is a must before being entrusted with bigger things. which leads me to my second thought...
2) perceptions of importance are not universal. just because a penny is worthless to you doesn't mean that it's worthless to everyone else... i'm sure benjamin franklin would have been more vocal than i was, demanding his four unreturned pennies back under the mantra of "a penny saved is a penny earned."