Rolling a cuboid - 2x1 box.

I watched a nice video tutorial about rolling a cube in Unity, which helped me a lot:

But I am rolling a cuboid instead - and it's a bit more work for sure. I have the rolling worked out, however my issue is one of error accumulation. I am rotating 90º in .5 sec and it's never exactly 90º - so at the end of the rotation I need to set it to what the rotation should be...
In the video he uses:

Code (CSharp):

1. Quaternion rotation = transform.rotation;
2.         Quaternion endRotation = rotation * Quaternion.Euler(rollAxis * targetRollAngle);

And then sets the transform.rotation to the endRotation after the roll is complete.
This works fine if I just roll the short way, but if I stand it up on end and then roll it back down it will sink into the floor like so:

I feel like it's the rollAxis in that calculation that is the problem. I calculate the roll point and use that in transform.RotateAround so that the rollAxis is at the rollPoint. But it's not being used here...
thoughts?

 

Realized I was getting the rotation from the manager object the script is on - and not the cube object I needed. Have it working much better now.

Code (CSharp):

1. Quaternion rotation = theCube.transform.rotation;