Well as far as the math goes, you can get 2 decimals by multiplying *500 instead of 50. Then change the SEROUT2 to divide by 100 and use DEC2.

But those references aren't really accurate enough to get that kind of resolution reliably.
And they drift some with temperature, so you'll probably want to stick with 1 decimal place.

You could also do the same thing with an external "Precision" reference and get better resolution. But of course that uses a PIN, which are precious on an 8-pin chip.