The only tax that applies to a purely domestic award on AA is the USD2.50AY security charge which is charged per sector. LGA-ORD-LAX is two sectors and so would be USD5.00 per person. Which is about EUR4.00 per person, EUR8.00 in total taxes, fees and charges.
The remaining EUR102.00 doesn't seem to be right - even if you did pay the service fee for booking over the phone, that would only come to EUR78.00.
I think you might have been charged some taxes that don't apply to a zero fare ticket. I'd call back and nicely ask them to look again.