I don't know what your fuse holder uses, measure the length of the old fuse.
Personally I would use a slo blow, since I'm pretty sure you are using this on the 110v side of the transformer.
If this is about a 24v transformer, and up to 10 amps, then it's about a 4:1 ratio, i.e. 4 times less current on the primary side, and 2.5 amps is right at the steady state current, and there's not a lot of margin for the momentary inrush, if you had a pretty good load on the output.
That's why I would go slow blow.