Bundled tied price

[PicknBite]

Hi
I need some help here. I am selling my products in bundled tied price and thus i do not need to display the price per product. For example, the customer can pick 10 item for $18, 15 items for $25.5 and 20 items for $32.
The final cart should just show the item chosen and the final price according to the preset pricing.
I am using ViruteMart 2.0.16

Please advise me how can i do it. Many thanks!