Mileage reimbursement for independent contractor

I was just hired as an independent contractor doing local pickups in the city near to me for our home office 1.5 hrs away. I will leave my day job driving to multiple sites within the city and ending at a shipping facility to send the items to our home office. I do not have a centralized office I am reporting to and my pickups may vary day to day as to where they are required. Do I calculate my mileage from my primary job until I reach my home (through all of the site pickups and the shipping facility)? Or do I calculate my mileage from the first site I arrive to until I reach the shipping facility? Thank you!