The input_number helper does not have an option to set the precision.
When you show an input_number helper value in a tile card for example, it will always round itself automatically.
For instance, if the value of an input_number is 21.5, it will show 21.5 in a tile card.
But, if you want to show that 21.5 as a currency value in a tile card, you would typically want to show 21.50 in the tile card.
As far as I know, this is not possible at the moment. It would be great if the input_number helper has a precision option just like the “combine the state of several sensors” helper for instance.