Hello - I had a customer point out that the tax calculation is being based on the billing address.

At least in WA State, the tax rates are calculated based on where items are being shipped to. If I buy something with a WA billing address but ship it to CA - I do not need to pay Washington state sales tax. Had the clients acctg dept confirm this with the dept. of revenue here.

Changed line 86 in tax.module from
$billing = $txn->address['billing'];
to
$billing = $txn->address['shipping'];

Might make sense to make this configurable for each tax - since it might be different in different locales.