This sounds like it does what you want. It is also fairly "manual", but what you want is pretty specific, so maybe that can't be avoided.
If you have a more general rule, like "I only want ticks greater than 3", then that could be put to use. However, you don't give enough detail to guess what you want.
y = [2 2.2 2.4 2.8 3 3.2 3.4 3.6];
x = y./2;
figure
plot(x,y,'.-')
set(gca,'YTick',[2.8:0.2:3.6],'YTickLabel',[2.8:0.2:3.6])
