Is it possible to have a process where a customer may incur a "small order" fee if they buy a product from a certain category?

For example, I sell car parts and tires and if you buy only 1 tire, there is a $5 small order fee, regardless of anything else purchased. So I want a "test" done on the shopping cart products and if the "tire" category contains only 1 piece, then the charge is incurred.

I'm thinking that it would be best to have a virtual product "small order fee" which gets added to the cart as needed. This way I have control over raising or lowering the fee.

Would it be best for future use to have the "small order fee" as an option for all items? This option would be ticked on or off in the product information input process.

Thanks for ideas!