Are raisins toxic to cats?

Hello,

On Monday of this week (today is Wednesday) my cat came up to me while I was eating some raisins and he was sniffing them so I gave him one. He played with it and ate it and I thought it was so cute because he's usually not interested in people food at all, so I gave him a few more...maybe 5 raisins total. This happened again on Tuesday and today. I thought it was odd that he liked raisins so much being that the only other human food he's ever eaten were some frozen peas that I spilled all over the floor one time, so I did a google search for "cats and raisins" and was horrified to find that raisins may be toxic to cats. He ate about 5 or so raisins three days in a row. He doesn't seem be exhibiting any symptoms of kidney problems, but it's hard to monitor his litter box situation as there is another cat in the house and I'm at work during the day so I don't know which one is using the box/how often, etc. Money is tight (huge student loan bills each month) so I don't want to pay to take him in for testing if there's no need - but if I should be concerned, I would like to take him in as I don't want him to experience pain or suffering. He is an older cat (about 13) and I understand older cats are at an increased risk for kidney troubles in general...I just hope I haven't hurt him by letting him eat raisins! I love this cat so much and I feel so bad that I may have unknowingly poisoned him! Do you think approximately 5 raisins a day for 3 days is cause for alarm and/or do you think I can just keep an eye on him for any symptoms of a problem and go from there? So far, I have not observed any unusual behavior (lethargy,vomiting, etc.). I appreciate your time and this service!