You can use angled box for tiled background? Didn't know that, will be useful!
The collision for the circular sprite is perpixle, so the bottoms are rounded off :P I'm not quite sure why it's jaggedy whilst moving along a slope, I thought at first it was the sprite moves and doesn't stick to the ground and is actually floating and falling a bit, but I realised that isn't the case since you can go at immense speeds and it remains stuck to the ground.
Not sure what to do about this :(