Remove zero balances in calculated fields and keep two decimal points.

I have a fillable form with auto calculations for costs.  The blank calculation fields show up as 0.00 in the field.  I need the blanks to be empty showing no zeros.   When they do enter a number to calculate, I need the results to show 2 decimals, such as $ 19.50.  I prefer to do this using a custom format field.  Right now I have the follwing in my custom format scrip:

if((event.value == 0) || isNaN(event.value) || (event.value == Infinity))
event.value = "";

This shows 19.50 as 19.5 and shows 55.00 as 55.    How can I get this to display correctly?