There are several methods of getting a rounded cake top.
First, you can use an additional egg white, and beat the egg
whites until they are stiff (not dry) before folding them into the
batter. Then bake at least half of the batter in a loaf pan. The
top should rise up, forming a dome much like a treasure chest.
Another method, also using a loaf pan. Bake two layers in loaf
pans. This time let's assume they do NOT rise up into nice round
tops, but bake flat. Turn the layers out of the pans, then, when
the cakes are completely cool, use a serrated bread knife to shape
one layer into a rounded shape. Put the layers together with icing,
then use plenty of icing to smooth out and further shape the
top.
A third - and easiest - method is to bake part of the cake in a
rounded pan. Coffee Cans are often used for this purpose. Grease
the can well or line it with parchment or waxed paper. Bake part of
the cake in the coffee can, then turn it out and cool it, then cut
one side off for a flat base, leaving the rounded top.