Assuming a train line where single-ride tickets are normally collected or cancelled manually by train crew circulating among seated passengers, and it is physically possible to use them later if they are not:
If one takes a ride for which one has purchased a single-ride ticket or equivalent, and for some reason the conductor does not cancel it, should one destroy the ticket, as one has in fact used the service which was paid for?
I doubt this would be considered a "ta'ut" in the strict sense, as it is part of normal operations that sometimes not everyone's ticket will be collected. I could hear how one would not be required to destroy it, as this is part of the transportation business, but that it would be ethically superior to destroy it. I could also hear that preserving one's money under these equivocal circumstances would also be ethically advantageous, not to mention practically.