I've known that if one is performing in a 'public' venue, SOMEONE has to be paying royalties and it is usually the venue that pays to either BMI or ASCAP ... I know of at least one case where a musician was playing in a coffee house for tips and either BMI or ASCAP told the owner that a fee had to be paid or performers could only perform 'original' music ...

I've just never thought of the need to pay royalties if I post something on line for others to hear ...