Appending to crontab with a shell script on Ubuntu

I'm trying to add a line to the crontab on Ubuntu. Right now, I'm doing `crontab -e` and editing the crontab there. However, I can't seem to find the real crontab file, since `crontab -e` seems to give you a temporary working copy. `/etc/crontab` looks like the system crontab. What is the path of the crontab that `crontab -e` saves to? Thanks!