If there’s one thing that businesses like in their costs, it’s predictability. When there’s a bill to pay every month, it’s easier to plan around it when you know exactly what it’s going to be. Charges associated with accepting credit cards have always been variable: A heavier month costs more in processing fees than a slower one, and that’s just the way it is. Square, the mobile payments start-up founded by Twitter inventor Jack Dorsey, is aiming to address that. Thursday it announced that it is offering its small-business customers a flat monthly fee of $275 to accept payments. Read the full story at All Things D.