Errors in financial calculations

[Richard121]

All, I attach (I hope) a very simple petty cash spreadsheet. All entries are either values in GBP and pence - ie only to two places; or additions and subtractions, which should, logically, be limited to two places. None of the entries are caused by division (or multiplication), which could cause values beyond the two places.
I have expanded the column width to show many places of decimals. Can anyone explain why Excel gets its sums wrong? (And then appears to correct itself.) And what can I do about it?


Thanks
Richard
0 Petty Cash 2015 Mk II.xlsx