Like Peter Lynch says, invest in what you know. It would be cool if your round-up could buy a fractional share of whatever business you shopped at. If that company isn't publicly traded, you could set a stock for it to default to.
So if I go to Chipotle, my round-up goes to a fractional share of Chipotle. If I go to my favorite local hole in the wall, my round-up would go to a fractional share of $SPY or whatever I set my default to.
I know Cash App and the Robinhood Cash Card both have round-ups to buy stock, but they only buy one stock. Anyone know a card that's more inline with what I want?
Not sure how they pull it off, but you can make fee-free trades of fractional shares on Robinhood. I believe other platforms support this as well.
Pretty much every brokerage offers fee-free trades, and they usually make money by giving you a slightly worse price (as in, slightly higher purchase price and slightly lower sale price), but that doesn't really affect most regular investors.