Just to note, this is the same behavior as adding a value in a currency field on SharePoint new item forms as well. You can even type text into a currency field before it is validated.
I have tested this on both Forms for O365 and on premise versions of Forms.
I can confirm that the currency field does not in fact display as currency on edit on both versions and you will need to apply custom java script to do so. You can find references online on how to apply custom java script to a field to change the formatting to currency on edit. Alternatively you can make a feature request to have this piece added to the product on our user voice site here: Customer Feedback for Nintex
However, on display I can confirm that it does not show a dollar symbol nor decimals and commas UNLESS you specify a number of decimal places in Office 365. In on premise versions it is displaying the currency field as expected on display mode as Andrew is seeing.
Here is the configuration for my column on my list (O365):
Here is the result:
When you change this from "2" to "automatic" you receive the following result:
I am currently investigating internally if this issue is a bug or a future implement for forms for O365.
Just an update on this issue, In O365 if you have Currency field type under repeating section, it does not display any input with the commas in the view mode even you set 2 decimal places it will not show any commas.
Having the same issue, using a repeating section so had to put a Nintex Single Line Textbox in and set it to currency. Regional settings is a problem(some use "." and some ",") This is a issue on mobile, so when typing in "22.50" and the region is not set to USA, it saves it as 2250. They need to fix this.
Same issue. Responsive form Nintex O365. Currency symbol is missing in the form field even though specified as currency format in SharePoint.