It's not actually charging those one dollar items. Using a credit card is a two step process. There's the authorization step, where a retailer reserves a certain amount of your credit limit. (Depending on the situation, this may reserve the actual amount that's going to be charged, or it may be a token 1$ just to see if your card's valid. It sounds like SE must be using the token 1$ pattern.) Then, once the purchase goes through, the retailer sends a follow-up message to the card issuer to change that reserved amount to an actual charged amount.

If your purchase didn't go through, then that second part of the process never happens and your card is never actually charged. But you may see the amount reserved by the authorization step show up as "pending" for a couple days. Without an actual charge, it will never go beyond the "pending" stage, and after two or three days the retailer's chance to follow it up with a charge will expire and the pending item will disappear from your account without ever impacting your balance. (Note: Even though it doesn't affect your balance, it does impact your remaining credit limit for those two or three days that the money is reserved.)