Review Time!
These are simple minigames, and there's really not much to say.
Roller Coaster is probably the least good game out of the two. The controls are rather odd, keyboard controls would be a far better option than clicking on the rails with your mouse. The only way there seems to make you complete the game faster is by collecting coins, and since both the rollercoaster and the coins move at a constant speed, there isn't really much room to improvement, making this the least replayable minigame.
Shopping Game is much better. Since you're the one dragging the items with your mouse, there's a ton of room for error, and as a result, a ton of room for improvement. I think making the prices of each item random was not a good decision, though. If they were the same every time, there would be much more room for consistency, which is also important to make a game replayable.
I'm honestly kind of impressed the minigames show you how long you've took to complete them, yet doesn't seem to invest into this idea strongly.
The concept of this minigame collection is quite interesting, I just think it could have been executed better, but overall, it's not bad at all.