US coins go 1, 5, 10, 25, 50, 100 (although admittedly 50 cent and dollar coins are rare). US banknotes (excluding the rare two-dollar bill) go 1, 5, 10, 20, 50, 100. As far as I know, there have never been a 25 dollar bill or a 20 cent coin. Is there a historic reason for this? Because it feels kind of weird that the two wouldn't match up in how they jump in value.
You can see a list of discontinued coins and notes here, but the reason why there's no motivation to create a new coin or note today is sunk cost. There's no reason to retool all of those cash registers, redesign all that software, and revise all those bank databases because of the billions of dollars of associated cost.