to create taxable and non taxable items, you need to have a new cart column to be used to distinguish them.
Create a new cart column named taxable.
for taxable items, set this column to 1 in the add to cart button.
For non taxable items, this column should be set to 0.
when creating your tax rule, use the trigger:
number of Items with a specific column value:
If the number of items where 'taxable' has a value of '1' is '>' a value of '0'
for the calculation:
Based on Items with a specific column value:
Total of 'TotalPrice where 'taxable has a value of '1' 'times' '<your tax decimal>'