Good catch, Don. I tested the formula with positive and negative numbers, but not with whole numbers exactly divisible by 5. The following works for positive or negative numbers and accounts for this situation:
if {table.field} >= 0 and
remainder({table.field},5) <> 0 then
(truncate({table.field}/5)*5)+5 else
(truncate({table.field}/5)*5)
-LB