Well, this is not completely true. Depending on the relations of the aim of the scope (or to be precise, the inclinometer), and the inclination of the base, errors are larger as you get near zenith..

For example, the scope is pointed due North, and the base is tilted, low on the east, high on west.
When the tube is horizontal, the error is 0. But as you rise the tube, since the axis of the altitude bearings is tilted, the scope will point a few degrees to the NE, allthough both the azimuth and altitude scale tell you that the scope is pointed at Polaris...

Same situation, the scope pointed due east or due west, you will not get any error when using a inclinometer, because the altitude axis is parallel with the ground

When I carefully level the scope, I always get the desired object inside a 1º field, using both az and alt scales printed on paper...