We have used the non-equilibrium Green's function formalism combined with a Tight-Binding and an Extended Hiickel Hamiltonian for the transport calculation of finite single-walled carbon nanotube systems attached to Au(111) metallic contacts. Findings have revealed the limits of the Tight-Binding approach regarding its use in the Carbon Nanotube context. Moreover, we have thoroughly investigated the channel-blocking effects provoked by interference from the metallic contacts as well as the changes in the transmission function caused by variations in the metal-tube interface geometry.