I'm not sure if this will work as it affects all area calcs, not just zones.
Under Options>preferences> dimensions you can set how many decimal points it will calculate the area to. There is also a check box for rounding.
Calculations round up once they are greater than 0.5.
HTH
Erika
Architect, Consultant
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
Mac OSX 10.11.1
AC5-18
Onuma System
"Implementing Successful Building Information Modeling"