In the link to Internal Exchange, the definition has
The internal exchange is a decentralized exchange (DEX) on the Hive blockchain. It is part of the base layer code. Here is where people are able to swap $HIVE for HBD and vice versa. It does use an order book similar to centralized exchanges.

There are no transaction fees associated with trades occurring on the internal exchange.
But isn't there a loss of 5% when converting Hive to HBD on the internal exchange? While that isn't a transactional fee, isn't there a cost of 5%? So, the net on the first year is 15% APR, not 20%?