Round Down to the nearest 5

jshea23 

Just in case, to cover negative numbers

=MROUND(A1,SIGN(A1)*5)

or

=ROUND(A1/5,0)*5

jshea23 

This could be (assume A1 contains the number you want to round):

=INT(A1/5)*5

This will always round to the previous multiple of 5 (i.e. rounding down). If your intention is to round to the nearest multiple of 5 it could be:

=MROUND(A1,5)