Price with tax field admin side

I am new to Hikashop, my problem is when I tried to add Price with Tax using 5 digits e.g 6.7034 and then save product it automatically convert it in 6.7, but i need to save complete amount e.g 6.7034 or 6.73111 any idea how i fix it?
Please check screenshot.

Hi Nicolas,
Thank you for reply.
in my store people purchased products in bulk quantity like 1000 products, so i need hikashop calculate price including tax properly like if product price is 5.540 so its price including tax is 6.703 but hikashop just calculate 6.7 it creates problem for me. can you guide me how i force it to calculate price including tax 6.073 intead of 6.7?

Thank You