The \Magento\Tax\Api\Data\GrandTotalDetailsInterface is implemented by the \Magento\Tax\Model\Calculation\GrandTotalDetails class

[dmitry_fedyuk (Dmitrii Fediuk)]

magento/magento2/blob/958164/app/code/Magento/Tax/Api/Data/GrandTotalDetailsInterface.php#L8-L8

magento/magento2/blob/958164/app/code/Magento/Tax/etc/di.xml#L62-L62

magento/magento2/blob/958164/app/code/Magento/Tax/Model/Calculation/GrandTotalDetails.php#L12-L15