Estimate, SO, Invoice is approved at various hierarchical levels based on two factors.

1) Discount offered against a product
2) Advance Payment

For a person at lower level in the hierarchy could approve transactions with lesser discount and advance payment. This freedom to approve changes when it goes to the higher level in the hierarchy. All customers wouldnt have to wait till all approvals are made by the head of department. Please create a more condition based purchase and sales approvals.