Checkbox in the cart (order processing) + 10%

[Menro]

Hello!
I have a task to bring the checkbox in the cart (order processing), when you click on that the total added 10% of the total order.

In my case it's furniture store, which has a service to assemble furniture - this service is worth 10% of the product cost. How can this be implemented?

Also need to display the cost of service in numbers to specify it in the order (email)