The past two times that I’ve been somewhere with a credit card fee, my credit card charge didn’t match up with what I actually wrote down on the receipt.

I base my 20% off the price and sales tax, but not that stupid fee, then round up to the next dollar. The first time, I was charged more to equal 20% including the fee. I went to a different place and decided to just go ahead and include the fee in my 20% plus rounding up. This time they actually charged me less. I did the math and they changed it to 20% based on only price and tax without rounding up.

I’m assuming it’s illegal, but how can restaurants charge a different amount than what I actually write on the check?

Edit: these are the final, posted, non-pending charges