I'm mostly honest except for with prices of certain things, like drum gear. My wife NEVER checks our balances and such in our accounts so there's a little bit of a 'wifey exchange-rate'. If a cymbal costs $250, then it's $149.00 to the wife.
Or, I use another trick if I feel like telling the truth. Example - I just bought a couple (cheap) overhead mics. They were $100 and if I were to tell her this right off the bat she might become pissed, so I'll completely exaggerate the price and say something like "Oh, they were only $299.00 a piece but they're really good." and she'll flip out. I let her flip out for a few minutes until she lets it all out then I say "I was only kidding, they were just $99." Then I'll show her the recepit and she'll say "Oh, really? Oh, okay." I don't use this one very often lest she'll catch on.