Do you guys count materials to "package" a package as part of shipping cost or should shipping cost only be the price paid to the shipping institution for shipping the package?

For example:

If to ship something you spend $4 on a tube/box, $3 for bubble wrap, and $3 for tape and $12 to the shipping institution, how much should you charge the buyer for shipping? I guess you could also add in do you count gas that it cost you to drive to the shipping location.

 

I wouldn't go as far as charge them the gas that it costs to drive to the post office. But I would say count however much the box, packaging materials, and shipping itself costs.