AVALARA will not help you decode their JSON. Here is the data I needed from a call to get tax rate:

tb = new Avalara\TransactionBuilder($client, "PF", Avalara\DocumentType::C_SALESINVOICE, 'ABC');
$t = $tb->withAddress('SingleLocation', $street1, null, null, $city, $state, $zip, 'US')
->withLine(100.0, 1, null, "P0000000")
->create();

$Arr = (array)$t;						

$tax=$Arr["lines"][0]->tax;
$state=$Arr["lines"][0]->details[0]->region ;
$county=$Arr["lines"][0]->details[1]->jurisName ;
$zip=$Arr["addresses"][0]->postalCode ;

$city= $Arr["addresses"][0]->city ;