The possible roots to check for would be -6, -3, -2, -1, 1, 2, 3, 6.
Using synthetic division to test should indicate 3 and -1 to be the rational roots.
Two more roots to find for the quadratic part left over from the two synthetic divisions (could be two irrational zeros).
3 | 1 -2 -5 4 6
| 3 3 -6 -6
|___________________________
1 1 -2 -2 0
-1 | 1 1 -2 -2
|
| -1 0 2
|________________________
1 0 -2 0