Harriet Baskas

Special for USA TODAY

You’re expected to tip your restaurant server a percentage of the bill and leave a few dollars per night for the housekeeper in a hotel.

But how much should you give the officer at the airport security checkpoint who pats you down and sends you on your way?

Trick question.

No tip is expected, yet in 2015 passengers in a rush to gather their belongings after going through airport checkpoints left behind more than three-quarters of a million dollars in the plastic buckets and bins.

That $765,759.15 was mostly loose change and, thanks to a law passed by Congress in 2005, once local TSA stations collect the cash and the TSA financial office counts it, it belongs to the agency.

“TSA makes every effort to reunite passengers with items left at the checkpoint, however there are instances where loose change or other items are left behind and unclaimed,” TSA said in a statement. “Receipts of unclaimed money are deposited into a Special Fund account so that the resources can be tracked easily and subsequently expended.”

Here are the totals of unclaimed cash that ended up in TSA coffers in previous years:

2014: $674,841.06

2013: $638,142.64

2012: $531,395.22

2011: $487,869.50

2010: $409,085.56

2009: $432,790.62

2008: $383,413.79

Passengers not interested in leaving an unintentional tip for the TSA can drop loose coins in pre-security collection boxes at Denver International, Phoenix Sky Harbor International and several other airports and have the money donated to a local non-profit.

Phoenix Sky Harbor installed spare change kiosks just before the city hosted the Super Bowl in 2015 and collected $11,833.37 to help with the operation of the airport USO that year. So far in 2016 (January and February) $1,715.50 has been donated.

Denver International Airport began its collection box program in 2013 and announced yesterday that, since the inception of the program, more than a quarter of a million dollars in spare change — $282,722 — has been donated by passengers to support Denver’s Road Home, a city program that provides services for the homeless.

Harriet Baskas is a Seattle-based airports and aviation writer and USA TODAY Travel's "At the Airport" columnist. She occasionally contributes to Ben Mutzabaugh's Today in the Sky blog. Follow her at twitter.com/hbaskas.