What do you believe is the single most important factor driving up the cost of living in Nigeria?

Three of the nation's largest retailers — Dollar General, Dollar Tree and Kroger — charge fees to customers who ask for "cash back" at check-out, amounting to more than $90 million a year, according to the Consumer Financial Protection Bureau.

Many retailers offer a cash-back option to consumers who pay for purchases with a debit or pre-paid card.

But levying a fee for the service may be "exploiting" certain customers, especially those who live in so-called banking deserts without easy access to a bank branch or free cash withdrawals, according to a CFPB analysis issued Tuesday.

That dynamic tends to disproportionately impact rural communities, lower earners and people of color, CFPB said.

Not all retailers charge cash-back fees, which can range from $0.50 to upwards of $3 per transaction, according to the agency, which has cracked down on financial institutions in recent years for charging so-called "junk fees."

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