Here is one approach:
% create plot
x=-10:2:10
y = x.^2
plot(x,y,'bo-')
% modify labels for tick marks
xticks = get(gca,'xtick')
scaling = pi
newlabels = arrayfun(@(x) sprintf('%.1f', scaling * x), xticks, 'un', 0)
set(gca,'xticklabel',newlabels)
