i tack em as straight as I can and mount them in the vehicle.
With a peice of chalk and a steady hand, barely touch the chaulk to the shaft (at each end) and have someone spin a tire. Where you see a chalk line is an out of round spot. Hit it with a hammer there and run the chalk line again.
Your looking for a full band of claulk around the shaft with no movement in your hand. That means the shaft is true at that end.
Do the same for the other side.
Now your 95% sure your in round.