Seems a contradiction

In my efforts to be a little greener, I adopted reusable canvas bags for grocery shopping. A couple of these are all I need since I am not stocking up the way my parents did with only one shopping trip per week and six mouths at the trough.

I noticed something odd after my last trip to the store. If I use my own bags, 3¢ is discounted from the final bill. That's swell. But this begs the first question: how are those three pennies charged when one is not supplying their own bags? I've never seen a charge for 3¢ on a receipt.

There is also another question. When I purchase just milk or just some other single item for which I do not need a bag, I am not credited 3¢. Why does the discount only kick in when I use my own bag?

I believe I am going to request the 3¢ discount the next time I buy items I carry out in my hands and I am a) checked-out by a manager at the register, and b) it is not crowded so we can talk about this without a line forming behind me. Stay tuned.