Doing a direct entry from a channel hold on a 536HP and SDS200 does allow 144.00250.
I can also add these with Sentinel and write them to the 536 (did not try the sds200) and they do stick when I look at them with the scanner.
Now if the scanner is actually tuning that frequency as entered is another story. I don't feel like hooking up a signal generator and running any tests.
I also tried 144.00750 and that works as well. So much for Uniden's step sizes but maybe they affect search ranges only?