Rounding mixed data types
One of the issues you face is that you can't mix data types within a single column. So while you can have numbers-as-strings in your varchar column, you can't easily do math-like functions on these strings-that-are-numbers.

However, with some casting and subqueries, you might be able to get the results you're looking for. The following works on SQL Server, though I'm not sure if it would behave the same on Access.

Here's a SQL Fiddle that demonstrates a solution, though it's probably far from ideal:
SQL Fiddle

If you run the inner query separately (

select
    value,
    case isnumeric(value)
        when 1 then round(cast(value as float), 0)
        else null
    end as valueint,
    case isnumeric(value)
        when 0 then value
        else null
    end as valuestring
from myvalues


) you'll see that it's selecting the raw value, a rounded number if applicable (otherwise null) and a string value if applicable (otherwise null), while the outer query is putting it all back together for you.

Hope this helps.