The rolling boil for 5 minute thing seems to be a belt-and-suspenders approach. The World Health Organization recommends bringing water to a boil as an indication that a high enough temp has been reached but all the bad bugs are dead after a few minutes at 160 deg F. Link
Not that's totally sterile at this point but anything that will make you sick is dead or deactivated. I figure by the time I see bubbles forming the water is safe.