Commuting rule
Travel between home and a regular workplace counts as personal mileage, not business mileage, regardless of distance.
Full definition
The first and last trip of the day usually fall under the rule when they start or end at home, so a drive from the house to the office is personal even when the employee stops to pick up supplies on the way. Trips taken between job sites during the working day are business mileage and stay reimbursable.
Where policies differ is the edge cases: a stop made en route, an employee with no fixed office, or a day that starts at a client site instead of the office. Reimbursing commute miles by mistake makes the payment taxable to the employee and weakens the audit trail for every other trip in the log.