Surely logging Hobbs is a somewhat dodgy practice anywhere, since it will include allowances for time before the brakes are on but the engine is running? Hobbs should only be used for what it was designed - logging engine running time.
There's no absolute rule of-course; personally I've logged to 5 minutes for years, although this year made a decision to switch to per minute - my personal decision, and completely unnecessary, but suits me.
A simple solution is that you keep your plog to the nearest minute, then just use the obvious conversion - 6 minutes = 0.1 hours. Round to the nearest 6 minutes (6, 12, 18, 24...), log to the nearest 0.1, problem solved.
G