Example: if you don't have access to anything but a Dish system, take a look at zap2it listings, which many use for their accuracy.
Two Broke Girls shows as starting at 9:01 and ending at 9:31. Dish's guide shows it as starting at 9:00 and ending at 9:30. Zap2it shows How I Met Your Mother Starting at 8:00 and ending at 8:31,which Dish's guide shows it as 8:00 to 8:30. Bones, OTOH, is 8:00 to 9:00 on both.
It would be a BIG help if Dish's guide had the actual start and stop times listed. At least then if you had a tuner that had to switch to start a new show, and the new show started at 9:01 and the show it was switching from ended at 9:01, it would get those right, even if it couldn't handle shows that end a minute after the new show starts.
You're 100% on this one... IF Dish is rounding down (as opposed to rounding up) then that would cause some problems too... and you're right, Dish could address this... though I wonder if there is an underlying reason why they don't do anything but 5 minute changes in the Dish EPG... maybe they've tried and it introduced more problems than it fixed?