Help with ROUND function

Hello,
I an having troubles with ROUND function, I am not able to round the result to the nearest 1/4
example
original formula =IF(N18>0,L18,IF(J18=0,0,IF(M18=0,R17,(((M18)*L18)+(R17*P17))/P18))) gives me a result of 1304.29
how do I round it to the nearest 1/4 so the result would be 1304.25?
cell M18 is 1
cell L18 is 1298.75
cell R17 is 1305.4
cell P17 is 5
cell P18 is 6

I have been trying but have not been able to succeed

Thank you

Thank you Olly
It works well, I was placing the ROUND function inside the formula rather than the beginning of formula.

Thank you once more for your time

Nino