I would like donations to be in increments of $25, with no upper limit. How do I do that without entering every $25 increment? ($25, $50, $75, $100, $125 and so on)

I am finding that when I enter a $25 increment and disable "Allow member to donate in any denomination." there is no option to pick $25 or any other amount. If I add a $50 option, they both show up, but the $50 option name is blank. If I then add a $75 option, the $50 option name appears, but the $75 name is blank. In other words, the name of the last increment is always blank. All in all, the amount/increment is a frustrating area.

There is not a way to limit the member to donating in specific increments and use the field for any denomination. In this case, I would simply do as you are already doing and clearly specify your wish to receive donations in the multiples of 25 and select the option for the member to donate in any denomination.