Nice. It is always nice to receive or even find silver! I have found 2 silver Quarters in Coinstar machines and 1 metal detecting in the past 6 months.
Very nice score! Receiving all three of those pieces of silver from the same till would have been enough for me to ask if there were more in the register. Never hurts to ask, although I can understand the excitement of hearing the distinct sound those made hitting your palm and not even thinking to inquire.
And if they'd come out of the self-checkout, I would've been looping around buying single items costing less than 26 cents (or, more realistically, $1.26) until I ran out of paper money. Edit: IF I hadn't had a grumpy child along...