@Jesse here helped me out with a bit of polishing and here is the end result. Hope it helps!
[Item Purchases:2, 1,1,1, 1]
>Items|QTY|Unit|Price|Total
@{REPORT INVENTORY TRANSACTION DETAILS:I.GroupCode,T.TotalPrice.sum.desc::{0}:,}
>>$1
{REPORT INVENTORY TRANSACTION DETAILS:T.Name,[T.Quantity.Sum],T.Unit,[T.TotalPrice.Sum]/[T.Quantity.Sum],T.TotalPrice.Sum.desc:I.GroupCode="$1"}
>Total||||{REPORT INVENTORY TRANSACTION DETAILS:T.TotalPrice.Sum.desc:I.GroupCode="$1"}
>>Grand Total||||{REPORT INVENTORY TRANSACTION DETAILS:T.TotalPrice.Sum}
