Include the custom Currency type into your Doctrine configuration.
Point a XML mapping driver to the vendor/michaelgooden/mdg-money-doctrine/config/orm/Money.Money.dcm.xml file to being using \Money\Money as an embeddable:
/**
* @ORM\Embedded(class="Money\Money")
*/
private $total;
/**
* @ORM\Embedded(class="Money\Money")
*/
private $tax;