I would recommend using PayPal Express Checkout for this and not PayPal Standard.
With express checkout, the user goes to the paypal site to enter the shipping and billing information, and is then returned to your site to confirm the order.
the shipping country will be stored in a session variable named "eCartCheckoutForm_shipping_Country"
you can use this session variable value when creating the shipping rules.
You'll need to create 6 shipping rules, 3 for domestic rates and 3 for international rates.
for the domestic rules, the triggers will be:
"Based on session Variable Value":
if the session variable "eCartCheckoutForm_shipping_Country" is "=" a value of "US"
then add another trigger for the price breaks:
AND
"Taxable Total For the cart"
if the taxable total price for the cart is ">=" a value of "0.01"
AND
"Taxable Total For the cart"
if the taxable total price for the cart is "<=" a value of "40"
the international shipping rules will be set the same way, except for the session variable triger will be set as:
"Session Variable Exists"
if the session variable "eCartCheckoutForm_shipping_Country" exist
AND
"Based on session Variable Value":
if the session variable "eCartCheckoutForm_shipping_Country" is "!=" a value of "US"
