Rounding of decimal numbers: Looking for an elegant way in latex table

That could be done by »siunitx«, which will also align the digits at the decimal marker.

\documentclass[11pt]{article}
\usepackage[T1]{fontenc}
\usepackage{caption}
\usepackage{booktabs}  % nice looking tables
\usepackage{siunitx}

\begin{document}
  \begin{table}[!htb]
    \sisetup{round-mode=places}
    \caption{Table caption}
    \label{tab:default}
    \centering
    \begin{tabular}{
      S[round-precision=2]
      S[round-precision=3]
    }\toprule
      1.98185942 & 0.14495331 \\ \bottomrule
    \end{tabular}
  \end{table}
\end{document}

The alignment of the digits is centered by default. The package manual shows you options for left or right alignment.

---

You could use pgfplotstable. You can pass the values directly as macro argument, or, since you are not rounding the values by hand (it seems to me that they are a kind of a measurement series), you can also load them from a csv or similar formated file.

\documentclass{article}
\usepackage{pgfplotstable}

\begin{document}
    \pgfplotstabletypeset[
        %col sep=&,row sep=\\, % to immitate the tabular
                              % the default is: space = next column
                              %                 newline = next row
        % global:
        precision=5,          % five digits
        % only for the first row:
        columns/0/.style={precision=3},
        dec sep align,        % align at the dec point, default is centering
        header=false,         % input data has no header
        every head row/.style={output empty row} % output has no header
        ]
    { % here could also be a filename with the following content
        1.98185942  0.14495331
        1.9         0.14
        19.8        14.49
    }

\end{document}

If you have more tables like that you can also define a style for them so you do not have to copy and paste everything:

\pgfplotstableset{my style/.style={precision=5,
            columns/0/.style={precision=3},
            dec sep align, header=false,
            every head row/.style={output empty row}}
        }
\pgfplotstabletypeset[my style]
{   %
    1.98185942  0.14495331
    1.9         0.14
    19.8        14.49
}

There a many more options! Simply take a look into the manual to adjust the solution to your needs.