Well let's think, I'm 21 now and I must of had that jar since I was 6. So that's 15 years. In that time I think I've emptied the jar 3 times, including this time. The last time was the first year of college, for me being 2001. So 5 years.
I think you'll find, having stayed up until 02:20 to stack it and bag it all (some fool decided to put it all on my bed...), there are no 10p pieces in there*.
*well, that's a lie, there were several, but I removed them and exluded them from the count - but before anyone changes their "bets", I also found a couple more coppers in my Dad's wallet, so I added them in too, thus evening things back out.