Some customers give tips and some do not. The drivers are not expecting them at every delivery, but they are greatly appreciated! A driver's work is physically demanding and they work in the heat, cold, rain and sometimes snow. If you feel like they did a good job for you, feel free to show your appreciation. Also keep in mind, the delivery driver may not be the same person as the pickup driver.
If you decide to tip the driver, most people tip between $5 and $20, with the occasional larger tip from exceptionally generous customers. The most common tip is around $10.