Here is a macro solution for you to consider, that is based on your flat text display.
Please TEST this FIRST in a COPY of your workbook (always make a backup copy before trying new code, you never know what you might lose).
1. Copy the below code
2. Open your NEW workbook
3. Press the keys ALT + F11 to open the Visual Basic Editor
4. Press the keys ALT + I to activate the Insert menu
5. Press M to insert a Standard Module
6. Where the cursor is flashing, paste the code
7. Press the keys ALT + Q to exit the Editor, and return to Excel
8. To run the macro from Excel press ALT + F8 to display the Run Macro Dialog. Double Click the macro's name to Run it.
' hiker95, 12/12/2017, ME1034963
Application.ScreenUpdating = False
Dim r As Long, lr As Long, n As Long, i As Long, tot As Long
lr = .Cells(Rows.Count, 2).End(xlUp).Row
For r = 2 To lr
n = Application.CountIf(.Columns(2), .Cells(r, 2).Value)
If n = 1 Then
.Range("C" & r).Value = .Range("A" & r).Value
ElseIf n > 1 Then
tot = 0
For i = r To r + n - 1
tot = tot + .Range("A" & i).Value
With .Range("C" & r + n - 1)
.Value = tot
.NumberFormat = "#,##0"
r = r + n - 1
Application.ScreenUpdating = True
Before you use the macro with Excel 2007 or newer, save your workbook, Save As, a macro enabled workbook with the file extension .xlsm, and, answer the "do you want to enable macros" question as "yes" or "OK" (depending on the button label for your version of Excel) the next time you open your workbook.