How to check given value is greater then or should be increment of 0.25 etc in php

I am facing some problem. Suppose i have value is :-

$value= 80

Now if user enter the value from form suppose less then 80 that i have checked with if else condition. Now i want these values to be accepted like:-

80.25,80.50,80.75,81,81.25,81.50,81.75,82 and so on means any value that exists 
anyvalue.25,anyvalue.50,anyvalue.75,anyvalue

Suppose if i enter these values like 80.10, 80.20,80.24,,etc and so on these value will not be accepted. Only values that contains .25,.50,0.75,will accepted. Hope you guys understand. Thanks in advance