Yes there is a cron job!
Start here for background reading: https://wiki.civicrm.org/confluence/display/CRMDOC/Bounce+Handling
I found all I had to do was to just follow the Documentation: https://docs.civicrm.org/sparkpost/en/latest/install/
Update Bounces are processed through a callback (no need for an email account dedicated to bounce processing), but CiviCRM only processes bounces for CiviMail-originated emails. CiviDesk is planning to extend bounce processing to transactional emails in the future as well.