This Article can describe how to assign default tax for each customer. Then when you input the customer on sales the tax will be automatically Assigned to that customer. In this case i want to set default tax for John he will get tax & service type tax instead of default to no tax. You can follow this article for more information.

I. Tax

You can see that I already have some of tax type

In contact i have a user named John and Maria here. I want to set John to have default tax to Tax and Service

As you can see after i assign John in sales the tax still on No Tax Option

II. Contacts

Step 1. Select the customer you want to assign

You need to click on his/her name 

You will redirected to this pages
Click edit button on top right corner

Step 2. Go to Preferences Tab

After you go into preferences page you can select which tax type you want to assign for John in here i want to set Tax & Service so every time John came he will be automatically have Tax and Service charge.

 And then click submit to save it.

Step 3. When John do a transaction , the tax type will automatically assign to Tax & Service