Thank you for your help!
I've actually read about the scaling and rounding issue on various other forums, but couldn't really wrap my head around it. This is how I set up the room:
And this is the view:
For the x and y placement of the textbox, I've used the round() function, because I thought that would solve the problem, but it doesn't so far. However, even though this bugs me a lot, I consider this to be a minor cosmetic flaw at the moment and will try to focus on other more important things.