What’s your version of SonarQube? I’m looking at our internal dogfooding instance and seeing the duplication percentage taken out to 2 decimals:
IIRC, the front end does (used to do?) some rounding before it displays duplication percentage. For more precision, you might consult the Measures page:
Notice that the rounded percentage displayed here is the same 0.0% you’re seeing on the project homepage, but the lower-level metrics tell the story.