People often say that but does the cost for handling cash really scale (even approximately) proportionally with the number of transactions or revenue?

Or is it more binary that you have to decide, you either handle any cash and have the cost associated with it, or you refuse to take cash at all? If the latter is the case, then avoiding cash altogether seems somewhat unrealistic where I am from. And if it doesn't scale then it makes a lot of sense cost-wise to try to do as many of your transactions with cash as possible.