Display the Tax Rate of the Selected Tax Item on the Customer Record

A custom entity field can be created which will source the tax rate. Please follow the steps provided below:

1. Navigate to Customization > Lists, Records & Fields > Entity Fields > New.
2. Label = Tax Rate.
3. Type = Decimal Number 
4. Under Applies To tab, tick Customer.
5. Under Display tab > Subtab dropdown, select Financial.
**This will display the Tax Rate on the Financial tab of the customer record. The Tax Item is located on the same tab.
6. Under Validation & Defaulting tab, set a default value of {taxitem.rate}. Tick Formula box.
**This is a formula to source the Rate field from the Tax Item.
7. Uncheck Store Value box on the Main field.
8. Save

To verify that it is working, edit one of the customer records. Go to Financial tab and assign a Tax Item then Save. In View mode, go back to Financial tab. Tax Rate should be populated.

Note that this would work only for Tax Codes set on the Customer record. This will not work for Tax Groups set on the Customer record.