SUM Account For Added Rows

I've created a simple budget sheet outlining various group expenses eg: Fixed, Flexible, Variable, and their totals sums.

How can I add all totals while still allowing for a new row to be inserted in any group?

eg:..............Row E

1........Fixed Expense group
2..................$20.00
3..................$40.00
4..................$40.00
5....Total sum $100.00
6.......Flexible Expenses group
7...................$10.00
8...................$20.00
9...................$20.00
10..................$10.00
11..................$50.00
12...Total sum $110.00
13......Variable expenses group
14..................$10.00
15..................$10.00
16..................$10.00
17..................$20.00
18..................$10.00
19....Total sum $60.00
20--------------------
21..Grand Total $270.00