Rounding a number via Nintex Workflow is a two-step process. Start by creating a “Single line of text” and a “Number” workflow variable.
Step 1 – Round the Number
Use the “Build string” action and configure it to use the fn-Round Inline Function. Set the action fields to:
Text = fn-Round({ItemProperty:Number})
Store result in = Text workflow variable
The {ItemProperty:Number} field can be an inserted reference of a value, item property or workflow variable.
Step 2 – Convert the Number
Use the “Convert value” action to convert the text value in Step 1 back to a number. Configure the action with:
Input = Text workflow variable
Store result in = Number workflow variable
You can then use the Number workflow variable within the rest of your workflow.
Update: There seems to be an issue with numbers greater than or equal to 1,000. I address this issue in my Number Rounding Using Nintex Workflow (Part 2) post.