You can run a "every 5 minutes" cron job on GoDaddy's shared server by doing this:
Create 6 jobs, each one occurs twice an hour: 00-30, 05-35, 10-40, 15-45, 20-50, 25-55.
Your cron job command should look something like the following (unless your directory structure is different of course):
/web/cgi-bin/php5 "$HOME/html/sendy/scheduled.php" > /dev/null 2>&1
Example of the first cron job
Make sure it says 'Enabled' under the 'Status' column, otherwise please enable your cron jobs