In case the pricing in Acumatica cannot work the way you need it to, there are some great additional pricing products that may be able to help with this functionality.   Rockton Pricing Management could possibly do this, allowing pricing to be driven by more than one line.  With RPM, pricing could be driven from multiple lines on the document, rather than just the current line, but the order of the line items are important when being entered on the document. If interested, you can check out the short video in the Acumatica Marketplace. This video may not show the discounts using multiple lines, but it gives you an idea about what the product can do.  You can also reach out to them to discuss your specific scenarios to see if this product would work for your needs before diving into a customization.

@Sai Chettiar 

There is no tiered functionality in Acumatica for what you are looking for. You would almost need a condition on the Sales Prices to state IF 10 were bought of this inventory item, then when 3 are bought of item B it would discount. 

I know it does not help right now, but you could create an idea for what Acumatica could add in the future. 

Agreed @kandybeatty49  Thats the situation right no. We are preparing to go ahead with a customization for now since the customer’s business needs this as a key requirement.,