How much should I report my sales on my tax forms?

I've begun selling antiques and vintage items in a small 10x10 space in a really great and affordable antique store. Other than Social Security, this is my income until I tap into my retirement account, probably several years from now.. Some items I buy I make great profits on when I sell them. Other items not so great. I'm trying to figure out what to declare on my taxes in terms of what I bought items for and what I sold for. I'm looking for an industry guideline of some sort. I keep records, but in this economy I need every dime I can get. I don't expect to make more than a few thousand dollars a year doing this. It's just to help pay for health insurance and so forth. Is the IRS going to come after me if I fudge a little?