help on round up

hi
I want help on round up as follow
e.g
33.25 must be 33.5 because it is greater than 0.25
33.13 must be 33 because it is less than 0.25
33.8 must be 34.0 because it is greater than 0.75
33.73 must be 33.5 because it is less than 0.75