The specifications of certain sums for certain items in the budget within any fund of the city shall not necessarily limit the expenditure in that fund to the particular item specified, but the money appropriated in the budget for a particular item in a particular fund if not needed for that particular item and if needed for other items within the same fund, may be expended for other items; provided, that the aggregate expenditure of that fund shall not in the aggregate exceed the amount fixed in the adopted budget for the year.