Simplest ending is the Awaken ending, achieved by not making a single sale; choosing the wrong dress for all customers. The day starts over again, just before the sale begins.
Individual endings are decided by the FIRST girl to make a sale by choosing the correct dress for the customer.
After making five sales, you unlock Jasmin, after 10 you unlock Karen. After finishing the endings of the other girls, you unlock Hannah.
Making 25 unique sales unlocks the secret, nude gallery. Finishing the game again, after reaching all individual endings, unlocks the harem ending and the epilogue.