Why does a donor have a Pending charge of $0.25,$0.50, or $1.25?
This is called a pre-auth charge (or pre-authorization charge).
This happens when a donor sets up a new payment profile.
When the giving site vaults new card information, it sends an authorization through for a negligible amount. The purpose of this is essentially a test to ensure that the card information submitted is valid. This is referred to as a pre-authorization. Unlike a normal authorization, pre-authorizations are not sent with instructions to settle the transaction in question. As such, this pending charge on the cardholder's account will fall off over time (usually 3-5 business days), and the charge won't actually go through.