> The problem with the grade-school rule is that, assuming the > last digit is uniformly distributed, you'll be rounding up 5 > times out of 9 and rounding down 4 times out of 9.
No, if the last digit is uniformly distributed, then 0 is as likely as any other. You round down on 0, 1, 2, 3 & 4 and round up on 5, 6, 7, 8 & 9. The fact that rounding down on 0 is the same as the unrounded number isn't significant.
