How do I determine the currency format of a calculated field?

You are referring to the form calculation field correct? I checked your form and it appears that you have set it up correctly. You were able to determine the form calculation to display the $ currency and show 2 decimal places.

You can add currency to the form calculation by inserting the currency in the calculation wizard.

For more information regarding form calculation, simply check out this guide: How to perform calculation in the form? 

Let us know if you need further assistance.