Progressive jackpots work by taking a small share of every stake and adding it to a prize that keeps growing until someone wins it. The jackpot meter on the screen shows that running total, and on networked games it rises with stakes from many casinos at once. A mystery progressive jackpot is paid at a random moment before the meter reaches a hidden limit rather than on a symbol combination, so any spin can trigger it.
Penny slots work on the smallest coin value a machine accepts, but almost no one plays a single penny. Each spin multiplies that value by the number of lines and by a bet level, so a penny slot with fifty lines costs fifty times its coin value or more on every spin. That is why penny slots are so expensive in practice: the headline value is small while the real stake, and the speed of play, add up quickly. How much a session costs follows from that per spin figure.
Progressive jackpot strategy mostly means knowing when a game is worth playing at all. Some players use a tracker that records jackpot sizes over time, or a calculator that estimates when a growing prize lifts a game's return above its usual level. Casino jackpot strategies of this kind can point to a better moment, but they cannot change the odds of a single spin, and chasing a big meter with money meant for other things is how sessions come undone.