Thanks a lot! I'm pretty sure it sticks to 160x144, but I do think the camera can move on subpixels, hence why certain objects can appear shaking, because on one frame they're in one position, then on another they're off by 1 pixel (which appears as a huge jitter on a scaled up 160x144 display). I'm not entirely sure what I can do about that, maybe ensuring the camera doesn't move on subpixels, but all the objects in the game also move on subpixels so I don't know if that would help.
But yeah, thanks for the detailed comment!