Ask yourself who cares ?
Just take it to the nearest 6 minute block, be it up or down. At the end of the day it is only a minor bit of adjustment. I have always used decimal logs and one day a 2hr 33 min flight may be logged as 2.6 hrs the next day it might be 2.5 hours. I am sure that over the course of the last 15,000 odd hours it all evens itself out in the end.
