Why Power Transmission In 11kV,33kV,66kV?

We know that there is some voltage drop due to the resistance of the transmission lines. For this reason, they transmit 10% extra voltage(10kV*10%=11kV). But we don't know the exact value of voltage drop as it depends on the value of current where the current is not constant i.e voltage drop may be less or more than the 10%. So, the engineer picks the nearest and appropriate fig as 10% instead of 7 or 13 or so on.But at higher voltage level transmission (400kV-800kV),the point of 10% is no more valid as voltage drop are compensated in these modern higher transmitted levels of voltage.