You want to know how to make only a portion of an item's value taxable.
- Create a Base Override rule
- list the percentage of the item value that should be taxable, you can list 0% - 200%
- You can make it apply to only one specific tax code, create additional rules for other tax codes
- If the item is not typically taxable in that state, you must also create a Taxability Rule:
- Choose Taxable = YES
- Use same tax code