Duplicate values in multiple rows - calculation problem

Hi,

ERP returns me a sales dataset that for each item in the order returns a row in a dataset, which specifies quantity, id and the rest... however this row also contains the total order value. So whenever I have an order with multiple items I get the rows populated with multiple duplicates of order totals. And therefore the sales report is insanely distorted. 

I am a novice in Power Pivot and my only way to solve this would be to create a duplicate dataset, which deletes all duplicates on the basis of OrderId and from there use the order total. 

But I think the more elegant solution would be with measures, however I do not know how to write it. Can any of you help me with this? 

The sample screenshot of the data is below:  

Thanks!

Andraz