Has an NHL game ever ended 10-5?
It has. 10-5 has been a NHL final 21 times in 70,352 games. The first was Montréal Canadiens beat Hamilton Tigers on February 16, 1921; the latest was Florida Panthers beat Boston Bruins on November 26, 1997.
That makes 10-5 the 57th most common final score out of 95 that have ever occurred in NHL. One point away, 11-5 has happened 11 times and 10-6 has happened 11 times.