Five kelvins. Just like five metres, no capital letters or funny symbols.
The reason you can do it for Celsius or Fahrenheit is that those are scales but not units. The energy in two bodies (with constant heat capacity) at 100° is not the same as in a single body at 200°, but if you use kelvins then it works out.
> We don't measure force in "degrees Newton"
Not for force, no, but: https://en.wikipedia.org/wiki/Newton_scale
Now that I think about, what's the etymological reason we use "degrees" to talk about temperature? We don't measure force in "degrees Newton" or electric current in "degrees Ampère". Why do we do it for Celsius and Fahrenheit?