According to Jim Recap: Anniversary
As their tenth anniversary approaches, Jim realizes that he hasn't purchased a gift for Cheryl, so he does what he has done every other year since they've been married - he gets Dana to buy it. The formula is $15 per year, plus he throws in an extra $15 since it's a round number for #10. Dana goes a little overboard, however, and buys a charm bracelet, with a charm for something special that happened each year that Jim and Cheryl have been married. It's a great present.
The only problem is that when Cheryl wants to talk about the wonderful things and how Jim came up with it, he can't remember what each thing represents and he's busted. It doesn't stop there, though, and it comes out that he's actually never bought a present for Cheryl in all the years they've been married. Then it comes out that he didn't even wrap it - he had Andy do it.
So to make it up, he buys Cheryl a big-screen TV. Of course, he's trying to get it for himself, but in the process, Cheryl uses it against him. She invites her friends over on Sunday to watch it while Jim is preparing to have his friends over for the game, that sort of thing. But before she knows it, she's sitting on the couch and putting off going to bed because she just loves it - what do you know? Jim actually got a good present.
