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Hi, 

There are several module options out there. The last module we used for one of our clients was :

https://addons.prestashop.com/en/combinaisons-customization/3129-fo-quantitydeclinations-prices-quantity-per-multiple.html#specifications

The module offers a minimal quantity approach as well the option to set certain prices based on quantity :

This means 

 it will allow you to set the minimum of 10 still allowing to buy 11, but you can set a special price at 20 

Take a closer look on the demo

I hope it helps.