begin{tikzpicture}
begin{axis}
  addplot coordinates {
  (100,200001)
  (200,200003)
  (300,200005)
  };
end{axis}
end{tikzpicture}

ytick = {200000, 200005, 200010}

yticklabel style={precision = 5,}

documentclass{minimal}
usepackage{pgfplots}


begin{document}
begin{tikzpicture}
begin{axis}[
      scaled y ticks = false,
      y tick label style={/pgf/number format/fixed,
      /pgf/number format/1000 sep = thinspace % Optional if you want to replace comma as the 1000 separator
      }]
  addplot coordinates {
  (100,200001)
  (200,200003)
  (300,200005)
  };
end{axis}
end{tikzpicture}

end{document}