What I forgot to mention is that the implementation of the degrees version of sin, cos, etc. is such that multiples of 90 degrees will result in exact values, that is: sind(180) = 0, cosd(90) = 0, sind(90) = 1.

This is achieved by reducing the angle to an interval -45 to 45 degrees first and keeping track of the quadrant (rotated over 45 degrees) in which the original angle lies. Then converting to radians and applying basic trigonometric formulae.

No such claim of exactness is made for other angles for which one or more of the functions yield a rational value.