According to my B737 Manual - Part B / Flying Procedures / Normal Procedures / Section 2.11.1 / Taxi In Procedure
After a 3 minute cooling period, and at aircraft weights below 46,000kgs, an engine may be shutdown to conserve fuel. If it is anticipated that more than 35% N1 might be required to taxi due to upslope or other considerations, do not shutdown an engine.
Keep both engines running on slippery taxiways.
I'm sure the crews of B757's / etc. have a very similar (weight specific) entry in the their manuals.