Hi He.Bill,
Input table with a column for each currency

A Header Row with the name of the currency. Body Cells are Number format. Footer Row shows the SUM of each currency.
Formula in Footer Cell A6 (and Fill Right)
=SUM(A)
You can add more rows to that table, and the SUM formulas will automatically adjust
Next table where you input the today's exchange rate (imaginary values, because they change daily). The world standard is the USA Dollar, so that is always 1.00
No formulas in that table.

Next table converts the sums for each currency to US$

Formula in A2 (and Fill Right)
=Input::A6×'Exchange rates to US$'::A2
Now SUM all the values to get a total in US$
Regards,
Ian.