# Compute the required details in a table using DECIMAL(38,2) for dollars and cents.
create or replace function bill( quantities, prices, taxrate) as table (
  with cte as (select sum(q*p) as subtotal
               from (select unnest(quantities) as q, unnest(prices) as p)),
  details as (select subtotal, subtotal * taxrate as tax,
                     (subtotal + tax ) as total
              from cte)
  select subtotal::DECIMAL(38,2) as subtotal,
         tax::DECIMAL(38,2) as tax,
         total::DECIMAL(38,2) as total
  from details
) ;

# The order and tax rate:
from bill ( [4000000000000000, 2],
            [5.50, 2.86],
            0.0765);