Another thing: Change your PSN password. That's a security measure that is often overlooked by most. Be sure to remember your new one, or write it down and keep it in a safe place.
Well I just found out the same thing has happened to me for about $30 in purchases. I called Sony and got disconnected then called my bank. How my bank works is that when I make a purchase immediately it's reflected in my account info. However if by the time money is added into my account it no longer accounts for the money that has been put on hold as being put on hold so if money wasn't taken out by the company I wouldn't know unless I checked the history (which I just found out today) thats why I am showing these purchases as being done today even though they were done last week. It sucks and it severely ticked me off.
Firepowerr is correct. Are you saying that you haven't purchased anything from PSN lately, or only that you haven't purchased anything that was exactly $5? If you have automatic funding enabled on your PSN account, and your wallet doesn't have enough money to pay for something; PSN doesn't debit your card account for the exact amount of your purchase. It rounds it up to a higher number. If you bought something in Home for $0.99, and you didn't have that much in your wallet; PSN would debit your credit card for $5. Not for however much change you were short. This is explained in the Playstation Store fine print.
A good idea is to check to make sure that PSN isnt saving your card info. You can check it right on your PS3. Goto Account Management > Account Information > Billing Information. If it has your card saved you can erase it. Also Account Management > Transaction Management > Automatic Funding and make sure its off.