if ($Number % 5 == 0){
   ...;
}

##</code><code>##

if ($Number =~ /^-?[0-9]*[05]$/){
   ...;
}

##</code><code>##

if ($Number % 5 == 0 and $Number >= 0){
   ...;
}

##</code><code>##

if ($Number =~ /^[0-9]*[05]$/){
   ...;
}