I wouldn't have lied, in the first place, since I don't believe in spousal allowances. If I want to buy something, I have the sense to know whether or not we can afford it; my dh feels the same way. However, since you did lie about it, I'd weigh my options very carefully. How much harm will it do now, to tell him you lied? Forget about "clearing your conscience" and think how it will affect his feelings and your relationship. Will he forgive and forget . . . or will it cause him to have trouble trusting you, in the future?
Another question - Is there a way he'll find out about your lie, if you don't confess? If he's going to find out, it's better coming from you. If not, I'd keep quiet and try to forgive myself for fibbing.