The Mround function will do what you want.
=Mround(1.25, 0.5) returns 1.5
MROUND
Returns a number rounded to the desired multiple.
Syntax
MROUND(number,multiple)
Number is the value to round.
Multiple is the multiple to which you want to round number.
Remarks
MROUND rounds up, away from zero, if the remainder of dividing number
by multiple is greater than or equal to half the value of multiple.
Examples
MROUND(10, 3) equals 9
MROUND(-10, -3) equals -9
MROUND(1.3, 0.2) equals 1.4
MROUND(5, -2) equals #NUM!