Populate A Spreadsheet Using Macro

A macro which compiles a list of entries and adds or summarises the cost.

Sheet1 contains multiple entries per group and a cost in ColumnB
Sheet2 contains only one instance of the group with a summary in ColumnB

Here's an example and I hope it helps;

Sheet1
A1 = November , B1 = 100
A2 = November , B2 = 50
A3 = December , B3 = 75
A4 = December , B4 = 10
A5 = September , B5 = 60

After running the macro with CommandButton1
Sheet2
A1 = November , B1 = 150
A2 = December , B2 = 85
A3 = September, B3 = 60