Haml syntax: split a line to a couple of rows

New lines can be placed after commas, according to the Haml documentation. So, perhaps something like the following would work:

%a.open-service{href: '#', 
                data: { service_name: service.description,
                        balance_type: "coinsurance",
                        total: service.a_total_billed - service.a_rejected - service.a_not_covered, 
                        discount: service} }