Returns the integer double value closest to this.
Rounds away from zero when there is no closest integer:
(3.5).roundToDouble() == 4 and (-3.5).roundToDouble() == -4.
If this is already an integer valued double, including -0.0, or it is not
a finite value, the value is returned unmodified.
For the purpose of rounding, -0.0 is considered to be below 0.0,
and -0.0 is therefore considered closer to negative numbers than 0.0.
This means that for a value, d in the range -0.5 < d < 0.0,
the result is -0.0.
Source
double roundToDouble();