tax configuration is one rule:
Triggers = Total number of items > 0
Calculation = Based on the cart subtotal
Cart subtotal times 0.10
I am setting up and testing on my local server so I can't give you a link. I have attached the file eCart1_PHP.php from the WA_eCart folder (this appears to be the cart object file).
Let me know if there's anything else I can do.