As mentioned here, Sam does experience temptation, but is able to resist (just as other characters like Galadriel could at least temporarily resist its temptations, though none had to endure it as long as Frodo and Gollum and presumably would have had their will broken eventually). Note in particular this quote from The Return of the King, in the chapter "The Tower of Cirith Ungol":
His thought turned to the Ring, but there was no comfort there, only dread and danger. No sooner had he come in sight of Mount Doom, burning far away, than he was aware of a change in his burden. As it drew near the great furnaces where, in the deeps of time, it had been shaped and forged, the Ring's power grew, and it became more fell, untameable except by some mighty will. As Sam stood there, even though the Ring was not on him but hanging by its chain about his neck, he felt himself enlarged, as if he were robed in a huge distorted shadow of himself, a vast and ominous threat halted upon the walls of Mordor. He felt that he had from now on only two choices: to forbear the Ring, though it would torment him; or to claim it, and challenge the Power that sat in its dark hold beyond the valley of shadows. Already the Ring tempted him, gnawing at his will and reason. Wild fantasies arose in his mind; and he saw Samwise the Strong, Hero of the Age, striding with a flaming sword across the darkened land, and armies flocking to his call as he marched to the overthrow of Barad-dur. And then all the clouds rolled away, and the white sun shone, and at his command the vale of Gorgoroth became a garden of flowers and trees and brought forth fruit. He had only to put on the Ring and claim it for his own, and all this could be.
In that hour of trial it was his love of his master that helped most to hold him firm; but also deep down in him lived still unconquered his plain hobbit-sense: he knew in the core of his heart that he was not large enough to bear such a burden, even if such visions were not a mere cheat to betray him. The one small garden of a free gardener was all his need and due, not a garden swollen to a realm; his own hands to use, not the hands of others to command.
'And anyway all these notions are only a trick, he said to himself.
And as Tony Meyer's answer pointed out, it may have been the effect of the Ring that made Sam "reluctant to give up the Ring and burden his master with it again."