Shop items cost what the user is willing to give

So my idea is really simple.
I have files on my Site, those files i want to put in my shop. I want that every User wanting to download these files has to register, that's why a shop-system is useful (still thinking about registration absolutely necessary)
The files will be added to the cart and at the end, there will be a checkout. Now here's the clue, at the end the user can enter the amount he is willing to pay for his downloads, if he pays nothing, that's ok. Maybe he should then be asked to like us at least in Facebook or sth else. If he is willing to pay something he enters the amount he wants to pay and then has his checkout possibilites.

So my question: "Is it possible to do this with Hikashop, that the user has the possibility to choose the amount he is willing to pay?"
Maybe i have not paid attention and Hikashop already has this option, in this case please let me know where it is

Thank you in advance!