How do you handle Item Samples & Item Bonus?

We operate a pharmaceuticals wholesale and distribution business and this involves providing free products to customers as:

  1. Sample
  2. Bonus
    Bonus items are calculated as a percentage based on order quantity of an item.
    For example if a customer orders 100 Pcs of a drug, we would provide 15 additional for free (15%). So basically the customer would receive 115 pcs for the price of 100.

My questions are;

  1. What is the best approach to handle samples?
    Should we create a sales invoice and apply 100% discount or shall we do this via delivery note or stock entry?

  2. What is the best method to handle bonus items?
    Is there a method to create such pricing rule? or shall we manually calculate the bonus percentage and then apply a 100% discount.

Any assistance is appreciated
Thank you