Where we have shared a meal, say split 5-ways, the hotel usually puts it down as 'dinner' and that is that. Whether you had the sandwich andhe had the lobster matters not a jot - you both pay the £25 and each UIN bears the same weight.
Where the bill is itemised and you shell out an equal amount then that is a little more difficult. You can then 'ring' your items that come near the average.
Tips are permitted in the civil service. However the military receipts only have to be retained for 12 months! In the CS it is 3 years.