Very minor difference on points

I recently made a purchase on Amazon amounting to $42.20. Since the Robinhood card pays out three percent cash back, that would come to $1.26.6, which rounding up comes to $1.27. I even got a notification saying I'd earned 127 points. When I look in the transaction history it says the same thing. Then when I got to redeem my rewards in the form of cash back it says I only have 119 points. I'm not that worried about eight pennies, but it's the principle of the thing. Also, what if it keeps happening? Eventually a few pennies becomes a few dollars and so on. Any ideas what might've caused this?