Show pricing by each, but force package sizes

Anyone know of an extension that will allow you to show pricing for products by the each, but sell by the package? For instance, my product is $0.10. I only sell by the package of 25. I need to show that the product's individual price is $0.10, but only allow people to order 25, 50, 75, 100, etc.

I have found custom unit extensions that allow me to set package size, but then the price is shown per package instead of per piece.