Catfish allows you to specify quantity batches in which orders can be placed.
E.g Customers can only order in quantity multiples of 35 (35, 70, 105, 140 etc)
To set this up, login as an Administrator
Choose Catalog -> Products -> Manage Products
Locate the product you wish to assign a quantity break to and edit it.
Click the Product Variant tab at the top, and edit the Product Variant
At the bottom of the Details tab you will see Order Pack Quantity. Enter the quantity breaks you require in this field.
If the user specifies a quantity which is not divisible by this number, they will see a warning on the Product Details page which will prevent them continuing
Please make sure the Minimum Tier Quantity is equal to the Minimum Basket Quantity.