I have a soldier with 51 TU.
In the quick grenade slot, the calculate cost of throwing a grenade was...
Throw Cost: 25 TU
Hands Full: 8 TU
Total Cost: 33 TU
However, when I actually try to throw the grenade straight ahead, the cost is 34 TU.
A soldier with with 65 TU is calculated to spend 40 TU tossing a grenade from backpack, but the actual cost is 41 TU.
Perhaps, the rounding method for calculating TU cost in the quick grenade menu is different from the rounding method used when actually throwing a grenade?