People are allowed to refuse cash for goods and services whenever they want for pretty much any reason other than discriminating against a protected class of people, including not wanting to handle cash as a form of payment. Amongst other things, this allows ecommerce to exist.

The legal tender laws just mean that if you offer a sufficient quantity of legal tender in settlement of debt, your debt is discharged and they can't sue you for non-payment. This ensures cash has value, and means that most shops will take most forms of cash, even if it means queueing up for counter service because the kiosks are card only

Legal tender is only required to be accepted for debts already incurred.

For instance, if you are at the bar and they pour you 3 drinks then ask for payment, they have to take your cash.

On the other hand if you are at the bar and, ask for a drink, and they say that'll be $10, they are not required to take your cash (the debt has yet to be incurred) and are also of course not required to provide you that drink if you pull out a $10 bill.

Of course, why wouldn't they?