in the cart object, you would need to have a column for ProductType
in the add to cart button, set the ProductType to mark the tax rate it falls into.
for example, if its tax rate is 10% set ProductType to 1, 12% use 2, 20% use 3, etc...
then on the tx tab of the eCart object, create a tax rule for each rate using the "Based on items with aa specific column value" calculation:
Total of 'TotalPrice' where 'ProductType' has a value of '1' 'times' '0.10'
Total of 'TotalPrice' where 'ProductType' has a value of '2' 'times' '0.12'
make sure the cart display is set to show the tax rules individually.