How to Add Rows to Ubuntu CronTab

For example ;

To restart nginx service every 5 minutes:

crontab -I | {cat; echo ''/5 * * * *  systemctl restart nginx''; } | crontab -

To add crontab script to mehmet user:

crontab -u  mehmet -I | {cat; echo ''/5 * * * * systemctl restart nginx''; } | crontab -u mehmet -