Some people will lose the whole $100 without a win some people will win $100 or more right away and walk away. The slot is programmed to have winning and losing spins come up randomly, but each a certain amount of times that will be realized over many, many spins.
The 95% example you gave is a theoretical amount that the casino should receive over the long run for every $100 run through the machine, the casino expects to keep $5 on average. I'm not a math guy, but I'll try to give you a short version, and let others correct it if necessary.
