The nearest 5 minutes is a 12th of an hour, the nearest 15minutes is a quarter of an hour. No one ever cares about a 10th of an hour (6minutes) i.e. the nearest minute or second so you inadvertently demonstrated my point. Also the "high precision in seconds" is also conveniently a base 60 system which also goes evenly into a full day, or week, or year despite none of those measurements being metric either.