Default values were introduced in 2021.10. Petro had written a recommandable post here.
Try to give the |float and |round filters a default value that fits to your needs, e.g.
|round(0,default=0)
and
|float(100)
|float('desired value', default='fallback value')
https://www.home-assistant.io/docs/configuration/templating#numeric-functions-and-filters