Numbers refactoring

My output looks like this:
Johnny Smith has a tax liability of $ 17600.0
Jane Doe has a tax liability of $ 26000.0
Liz Lemon will receive a refund of $ 21000.0
First Name Orsillio will receive a refund of $ 1600.0
Eric Schmidt has a tax liability of $ 15120.000000000002

I was going to change it to .00 with number.to_s.reverse.gsub(/(\d{3})(?=\d)/, '\\1,').reverse

but I get this error:

main.rb:17:in `<': comparison of String with 0 failed (ArgumentError)
	from main.rb:17:in `block in <main>'
	from main.rb:16:in `each'
	from main.rb:16:in `<main>'