Praise be to Allah, peace and blessings be upon His Messenger.
Islam has forbidden bribery, and Allah has cursed, by the tongue of His Messenger, the bribe-giver and taker. Abdullah Bin Omar was reported as having said: “The Prophet (PBUH) cursed the bribe-giver and taker” {Al-Tirmizi in a sound Hadith}. The forbiddance of bribery multiplies once it leads to eating up other`s money and rights unjustly, or inflicts injustice on them. Therefore, one who seeks repentance from Allah for committing this major sin should ask for forgiveness, be remorseful, and never commit such an act again.
One who took a bribe while being entrusted with a public position should give it back to the state`s treasury. In the Hadith: “Allah's Apostle employed an employee (to collect Zakat). The employee returned after completing his job and said: "O Allah's Apostle! This (amount of Zakat) is for you, and this (other amount) was given to me as a present." The Prophet said to him: "Why didn't you stay at your father's or mother's house and see if you would be given presents or not?" Then Allah's Apostle got up in the evening after the prayer, and having testified that none has the right to be worshipped but Allah and praised and glorified Allah as He deserved, he said: "Now then ! What about an employee whom we employ and then he comes and says: "This amount (of Zakat) is for you, and this (amount) was given to me as a present'? Why didn't he stay at the house of his father and mother to see if he would be given presents or not? By Him in Whose Hand Muhammad's soul is, none of you will steal anything of it (i.e. Zakat) but will bring it by carrying it over his neck on the Day of Resurrection. If it has been a camel, he will bring it (over his neck) while it will be grunting, and if it has been a cow, he will bring it (over his neck), while it will be mooing; and if it has been a sheep, he will bring it (over his neck) while it will be bleeding." The Prophet added: "I have preached you (Allah's Message)." Abu Humaid said: "Then Allah's Apostle raised his hands so high that we saw the whiteness of his armpits.” {Narrated Abu Humaid As-Sa'idi}.
If the bribe-giver got the bid with more than its actual cost, or didn`t do his job as required, then this is considered infringing on public funds which makes it incumbent on him to seek repentance from Allah, and give back rights to those to whom they belong. He is obliged to settle the matter by giving whatever is due on him to the treasury. The Messenger of Allah said: “Some people spend Allah's Wealth (i.e. Muslim's wealth) in an unjust manner; such people will be put in the (Hell) Fire on the Day of Resurrection” {Bukhari}. And Allah Knows Best.