Can't convert string to float because of '.'?

I need to round the string values of a column in my dataframe up to 2 decimal cases, so I started by converting them to floats using astype(float) and then using round(2).
Ex:

df['col'] = df['col'].astype(float).round(2)

But I’m getting the following error:

ValueError: could not convert string to float: '.'

I thought the dots would be no problem, is there something I’m missing here?

Edit: It’s a huge amount of data, so there could be unexpected values, but after filtering it to testing samples the error continues.

Edit2: Turns out I still had invalid data even after filtering the sheet, so sorry for the seemingly dumb question lol. mozways’s solution worked fine.

>Solution :

To convert string to numeric without errors upon invalid data, use pandas.to_numeric:

df['col'] = pandas.to_numeric(df['col'], error='coerce').round(2)