Ok, you can give a name to each plot and combine them with Show
:
For[j = 0, j < 5, j++,
Anstot1 =
NDSolve[{0.5 Derivative[1][\[Sigma]x][t] + (
k[t] \[Sigma]x[t])/\[Gamma] == ftot[t], \[Sigma]x[0] ==
ini}, \[Sigma]x, {t, 0, \[Tau]}];
ini = \[Sigma]x[\[Tau]] /. Anstot1;
pl[j] = Plot[\[Sigma]x[Mod[t, \[Tau]]] /. Anstot1, {t,
j \[Tau], (j + 1) \[Tau]}]
];
Show[Table[pl[j], {j, 0, 4}], PlotRange -> All]