You can surround your reference to the {Cost Bias} field in a ROUND() function:
<the rest of your formula> ... & ROUND({Cost Bias}, 2)
As to this:
This is true for all number fields in Airtable - the formatting applied to number values of any type displayed in a field is just that – only formatting. Behind the formatted number, the fields are always holding a precise (exactly how precise I don’t know) float. It’s probably a good thing, as, in the long run, it provides the most flexibility and accuracy to calculations chained through multiple formula fields. And it gives you the control over when and how to round values.