I had presumed the '2' was intended as '20' but had to go to lunch so Star beat my example :) But, the following that had prepared excepting for a typo should resolve the question raised in the follow up--
dn=datenum([1993:2016],1,1).'; % a set of datenums over some 20+ yr
y=rand(size(dn)); % and some dummy data to go along...
plot(dn,y)
yr=datevec([dn(1) dn(end)]); yr=yr(:,1) % get the actual year range
dt=datenum([yr(1)-mod(yr(1),5):5:yr(end)],1,1); % years modulo 5
set(gca,'xtick',dt) % and set the tick marks at those dates
xlim([dn(1) dn(end)]) % now set x limits to range of x dates
datetick('x','mmmmyyyy','keeplimits','keepticks') %to date display
NB: 'keeplimits','keepticks' will prevent the automagic prettifier from futzing around with the values you've asked for. The full month may turn out to be too long for as many ticks as you've asked for; the 'mmmyyyy' format may work better, but you'll have to judge how it looks...
