Lulzbot states that the TAZ6 has 250mm of Z-travel, and that is what it says in Cura. But I needed to print a 254mm tall object.
A quick check of the actual Z travel of the Taz6 showed 257.2mm of travel. Just home it out, then manually move the Z up until it hits the endstop. Then just change the Z-travel in the Cura machine setting.
Now it is possible that other TAZ machines may have slightly different assembly tolerances, so be sure to check your actual Z travel.