Honesty is certainly the best policy, but it doesn't always provide the best results. A few years ago my wife and I spent 4 days in the US. Like you, I'm somewhat anal about keeping track of all my purchases abroad and I had a detailed list and receipts for everything. Coincidentally, our purchases equaled our allowable combined exemptions (and no single item exceeded either personal exemption). I filled out the declaration card and showed the maximum allowable claim for each of us. My wife was not comfortable doing this as she (correctly) figured being honest in this case would just create problems. She actually suggested we fudge one way or the other a little bit, but I stuck to my guns.

Upon going through customs we were directed to secondary and the agent asked to go through our luggage. I became a little irate (no yelling or screaming, just firm forceful discussion) about being harassed for being honest. I then pulled my list and receipts out of my pocket and told the agent he was welcome to check my math. He glanced at the paper and then told us were good to go.

Since then we've both acquired Nexus cards and find the process much more civilized and not subject to the whims of a cranky agent.