@lithander, did you tried ROTSPRITE?

... it actually do A REALLY DECENT (better) result than the photoshop scale/rotation. I have about 12 years using photoshop and i though the rotation/scale was decent, but ROTSPRITE actually do a LOT BETTER JOB!... so, if your loocking for rotation/scale QUICK, ROTSPRITE would be defenily the first option.

And... as Dusty said...

...If you work with an image 1000x1000 pixels large, rotating and such is no problem because it has a lot more data to work with. However, an image 32x32 pixels large only provides so much data for the algorithms to work with, so it's a lot easier to mess up....

so, bigger images works better for rotation and scale. And... if you scale x2.x3.x4.x5 and so on, you will be always in the safe place. Now, if you GO DOWN, you will start to get problems with the "new pixels" since the algorithm will put pixels mathematically. Also remember than pixelart is the smaller extent. So knowing this you will understand than some pixels will not exist or will appear a new ones, this if you go from bigger to smaller. And, Rotations with numbers with decimals will get problems for the altorithm too, so to be on the safe zone with rotation, try to use... 90/70/50/30° or numbers with no decimals or sharps angles.