EPGAP is a fraction, so you can set it to any value between 0.0 and 1.0. (If the acceptable gap is large, the MIP will terminate sooner.)
You can find some documentation here.
From the CPLEX 10.0 PARAMETER Reference manual
CPX_PARAM_EPGAP
EpGap Any number from 0.0 to 1.0
mip tolerances mipgap Default: 1e -04
Code: 2009
Type double