Jagged edges when rotating straight line with nearest neighbour

In that case, depending on what the design looks like, this would probably be better done in Illustrator. 

If the image is rectangular, as in your example, you could create it as a shape layer using the Rectangle tool. Then when you rotate the edges should be uniform.

That's been a problem in PS for years.

If your objects are just a solid color, you could do this: Make a selection of your object, and go into Quick Mask mode. Rotate the Quick Mask channel with something other than Nearest Neighbor, like Bicubic.

Still in the Quick Mask channel, Image > Adjustments > Threshold. As you adjust the Threshold slider, you will see some sweet spots where the edges aren't jagged. Commit the Threshold, and exit Quick Mask. In a new layer, fill the selection with the desired color, and hide the original object.

You could also do the same sort of thing to the Layer Mask of a Color Fill layer.