Quote from the spec:

The computed value of the property is calculated by rounding the specified angle to the nearest quarter-turn (90deg, 100grad, .25turn, etc.), rounding away from 0 (that is, 45deg is rounded to 90deg, while -45deg is rounded to -90deg), then moduloing the value by 1 turn (360deg, 400grad, etc.).

As to the rounding away from 0, the example says that -45deg is rounded to -90deg. What about 315deg (the equivalence of -45deg)? Should we round it to 360deg (equivalence of 0deg) to align the rounding away from 0 stuff? This is a bit confusing to me.

If we intent to always make -45deg (and 315deg) always round to -90deg, then IMO this worth some more words in the spec. Since there are only four possible rounding edges (45deg, 135deg, 225deg, 315deg), maybe we could also specify all of them in the spec. instead of just putting 2 examples.