here is Plugin changes for eshop to tax on shipping

if (!function_exists('eshop_get_tax_rate')) {
        function eshop_get_tax_rate($band, $pzone){
		global $wpdb, $blog_id, $eshopoptions;
		$area='country';

		if('yes' != $eshopoptions['hide_shipping'] && (isset($_SESSION['shiptocountry'.$blog_id]) && $_SESSION['shiptocountry'.$blog_id] == $eshopoptions['location'])||(isset($_POST['country']) && $_POST['country'] == $eshopoptions['location'])){
			$area='state';
		}

		//if(isset($_SESSION['shiptocountry'.$blog_id]) && $_SESSION['shiptocountry'.$blog_id] == $eshopoptions['location'])
		//	$area='state';

		//rehash the zone to make sure we're picking up the correct tax rates!
		$tablecountries=$wpdb->prefix.'eshop_countries';
		$tablestates=$wpdb->prefix.'eshop_states';
		if($area=='country'){
			if(isset($_POST['ship_country']) && $_POST['ship_country']!='' && 'yes' != $eshopoptions['hide_shipping']){
				$pzoneid=$_POST['ship_country'];
			}elseif(isset($_POST['country']) && $_POST['country']!=''){
				$pzoneid=$_POST['country'];
			}
			if($eshopoptions['etax']['zonal']== 1)
				$pzone=$wpdb->get_var("SELECT zone FROM $tablecountries WHERE code='$pzoneid' LIMIT 1");
			else
				$pzone = 1;
		}else{
			if(isset($_POST['ship_state']) && $_POST['ship_state']!='' && 'yes' != $eshopoptions['hide_shipping']){
				$pzoneid=$_POST['ship_state'];
			} else if(isset($_POST['state']) && $_POST['state']!=''){
				$pzoneid=$_POST['state'];
			}
			if(isset($pzoneid))
				$pzone=$wpdb->get_var("SELECT zone FROM $tablestates WHERE id='$pzoneid' LIMIT 1");

			if($eshopoptions['etax']['zonal']== 0)
				$pzone = 1;
		}
		$ratetable = $wpdb->prefix.'eshop_rates';
		$band=$wpdb->escape($band);
		$zone='zone'.$wpdb->escape($pzone);
		$taxrate = $wpdb->get_var("SELECT $zone FROM $ratetable WHERE id > 0 && class='$band' && area='$area' && rate_type='tax' ");

		return $taxrate;
}
}
?>

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http://wordpress.org/extend/plugins/eshop/