Pack in decimal amount

Our client has the following needs: if sell over a certain amount of product the unit value of each unit decreases, which they call "virtual pack".

For example, if they sell 6 units of soda, they transform this in a pack of six units with a lower average price per unit.

But if they sell 7 units, they continue applying the same lowest price for all the 7 items, generating a pack (virtual pack) with 7 units. How is impractical to have a pack item code to each pack with 6 or more units, I wonder if we can use decimal amount for packs.

Example: 6 units = 1 pack