When the user select s a state on the checkout page and pots to the confirm page, a session variable is create to hold the select ed state:
on the confirm page, open the server behaviors panel. Double click the eCart object server behavior, it will be the first in the list, to open the eCart object editor.
On the Tax tab create a new tax rule.
Set the Triggers to:
If Session Variable exists "eCartCheckoutForm_state_province"
based on Session variables value-
If the session variable "eCartCheckoutForm_state_province" has a value "=" to "CA"
Replace CA with the state abbreviation you wish to use.
For the calculation use:
Based On Taxable Subtotal
Cart Taxable Total 'Times" "<your tax rate>"