Does this mean a coming bigger problem in my marriage?

My husband and I live on a tight budget. Sometimes (esp. lately with hours being cut) really tight. There are times when groceries are a big expense we can't afford, and I have to make cuts just to get thru till next payday. I handle the jiggling of bill payments and the grocery budget (at his request) and we have a mutual agreement that neither of us will spend any significant amount of money without first discussing it with the other. When things are really tight, it can be pretty miserable and stressful for us both. I know that I don't like not having money to go out and buy what I want, even sometimes things that used to be necessities like makeup or the "better" shampoo. So I know he must feel the same way. Because of transportation issues, he sometimes does the light shopping for groceries, and it seems like he ALWAYS buys something that wasn't on the list. Always candy or other novelties like that, especially soda. The thing is, he doesn't realize how that stuff adds up. To most people, a few dollars for a 12 pack of coke isn't a big deal, but when you're choosing that over staples you otherwise can't afford, it is. Especially if it happens often. But at least I KNOW about that afterwards. Now I find out he has used the debit card to buy an XBox game. He says the money for the game was a gift from a friend, but what troubles me is that he deliberately didn't tell me about it because he thought I would get mad. First off, he's wrong, I wouldn't have gotten mad. But now I am upset, because he feels like he has to lie to me. I don't want to be a control freak about money and I hate when EITHER of us can't buy something. But he makes me feel so bad, because I DO have to say something, or he will just spend whatever and it can really make a difference financially. The biggest issue I have, however, is he feels like it's acceptable to lie to me, even necessary. The reason is because I feel that if he will lie about little things like this, how can I trust him with anything? Am I wrong to think that? I don't think I could live with a marriage that was lacking trust. So, is this just a case of my "over policing" him, or is this a sign of a bigger trust problem to come? What's your opinion?