I tell time by the 5 minute, that is, if it's 7:18 and someone asks me what time it is, I tell them it's 7:20. I know people who tell time by the 10 minute, and I even know people who tell time by the half hour.
And then I know the people who insist on knowing what time it is, really. As in, if it's 7:29, they need to be told it's 7:29. My best friend was like that. We were quite the opposite when it came to time telling, to the point that he'd go and verify the time whenever he'd ask me what time it was and I told him a number that ended in a 5 or 0.