That's not how the art of negotiation works though is it? You have to find the middle ground, you can be savvy without being insulting.
When a deal requires two parties to come together it doesn't have to be extremes, like I said that's poor business. I wouldn't offer a penny over and I wouldn't offer £50. I'd looked to establish a comfortable middle ground that would see the transactions successfully over the line.
You've poisoned your own argument by stating that by offering in excess the bartender may take offense, so naturally the same would be true in the opposite extreme, i.e. offering a penny.