I saw this while browsing around and I see it is a bit older. I think this might help quite a few so I'm going to make a new post with the information but I wanted to make sure people who contributed to this thread see it.
I provide admin services to Jobber users and I have a client that had this problem a while back. I think I have the solution to everyone's question. Here is how we did it:
Go to your tax settings and create a TAX RATE. Name it whatever you want to call your added fee (convience fee, processing fee, whatever but remember customer's will see this name) and put in the percentage. Then go back to tax settings and create a TAX GROUP. Now you can link together your regular tax and the convience fee by putting them in a group. Whatever you name this tax group will not be visible to customers.
Now when you are editing the quote/job/invoice you can chose what tax you want added to the subtotal by clicking on the tax name. So you can easily and quickly add CC fees or choose your regular tax fee if they are paying with cash or check. All tax rates and tax groups from your tax settings will be listed here.
As you can see, it automatically adds the appropiate percentage to the total so you can charge that through Jobber Pay.
I hope this helps! You can make as many groups as you need depending on your situation. This is also how you would charge both state and county tax for those areas that might have that although I'm sure you already figured that out.
