I just realized how perfect an illustration of what I'm talking about your pocket change example is.
If we go to the store to buy snacks, and in line for the counter I ask you how much money you have on you and you say, "I've got about a buck in change", I'll probably say "OK, gimme the buck and I'll cover the rest."
If we then walk out of the store and you say, "Oh, wait, I want a Coke" and pull out another dollar for the Coke machine, my reaction is going to be "Dude, WTF did you lie to me?" because it seems like you're just being a cheap *******.
If back in the store you'd instead said "I think I have about a buck in change", and then outside said "Wait, I've got another dollar in my jacket pocket... you want it or can I grab a Coke?" I'll just say "Don't worry about it, grab the Coke." because you were clearly stating an opinion and opinions can be wrong.
And if for six ******* years you pull that same **** on me by claiming you have less money than you actually do when it comes time to pay for something, I'm going to start calling you a liar. Because you ******* are.