If what you want is:
Qty 1 = $5.00
Qty 2 = $7.00
Qty 3 = $9.00

etc. etc. etc. ...

What you really want is Item Rate and set the charges for ...
Handling: 3.00
Shipping Cost: 2.00

Now you will get:
Qty 1 = $3.00 + $2.00 * 1 = $5.00
Qty 2 = $3.00 + $2.00 * 2 = $7.00
Qty 3 = $3.00 + $2.00 * 3 = $9.00

etc. etc. etc. ...