Postgres row_to_json precision for numeric type
You can round the values: 

select row_to_json(t)
from (
  select id, 
         round(value_1, 2) as value_1, 
         round(value_2, 2) as value_2
  from test
) t;


If you need that more often and don't want to type it all the time, create a view that returns the rounded values.