you would need to create a tax rule for each state using the eCartCheckoutForm_shipping_state_province session variable.
for example, to charge 6.25% tax for Mass, you would create the Tax rule as:
Name: MA Sales tax
Triggers:
"Session Variable Exists"
Session variable Name: "eCartCheckoutForm_shipping_state_province"
AND
"Based on session variable value"
If the Value of the session variable "eCartCheckoutForm_shipping_state_province" is "=" a value of "MA"
Calculation:
"Based on cart's taxable total"
Cart taxable total "times" "0.0625"
the calcualtions for other states will be done the same way, just substitute "MA" for the state abbreviation and "0.0625" for the tax rate for that state.