I'm the opposite on the bar tab thing. I like taking my receipts and cross checking them against the final bill. E-tab is too easy to slip a few extras on the final tab, and most people probably wouldn't question it thinking that maybe they did have 13 drinks instead of only 10.
It's no different than like at the grocery store when you know the shelf said the price was $1.90 and it rings up $1.95. Most people just say "oh well" and let it go. Either they don't want to bother over a nickel or are too embarrassed to tell the cashier to correct it. But a nickel adds up to the store if every customer walking through the store that day gets over charged.