Single Product Gratuity

[mdtdesign]

Is there a way to add a gratuity percentage to just one product category and not to the other categories and sub-categories? I need to have a gratuity that is added to only a particular category with it's sub-categories so that when a customer purchases that product online an automatic gratuity is added to the cart (of course, listed as a gratuity so that customer knows what that charge is for). I have searched the contributions and the forum for direction but have not been able to come up with a solution. Can anyone help or direct me to a solution?

Thanks,