Magento 2 Product Tax Class – Understanding Taxable Goods

The tax is calculated per item, so you have to set "Taxable Goods" for each simple product not for the bundle itself.

I use this in a plugin but shoud work in every class:

<?php
namespace Vendor\Module\Plugin;

use Magento\Tax\Api\Data\TaxClassKeyInterface;

class PluginName
{
    ....

    public function __construct(
        \Magento\Tax\Api\TaxClassManagementInterface $taxClassManagementInterface,
        \Magento\Tax\Api\Data\TaxClassKeyInterfaceFactory $taxClassKeyDataObjectFactory,
        \Psr\Log\LoggerInterface $logger
    )
    {
        $this->taxClassManagementInterface = $taxClassManagementInterface;
        $this->taxClassKeyDataObjectFactory = $taxClassKeyDataObjectFactory;
        $this->logger = $logger;
    }

    ....

    public function getTaxClassId($clasName){
        $taxClassId = $this->taxClassManagementInterface->getTaxClassId(
            $this->taxClassKeyDataObjectFactory->create()
                ->setType(TaxClassKeyInterface::TYPE_NAME)
                ->setValue($clasName)
        );
        return $taxClassId;
    }

    ....
}