All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Your statement, “There is an unwritten law that a 10% to 15% of procurement value is given to government procurement officers as a bribe,” either means that the government entities authorize their employees to take those commissions and claim them, or it means that this is part of the corrupt customs and traditions and that the government entities do not legalize it nor know of it. Anyway, bribery means anything that is offered for the invalidation of what is rightful or the endorsement of what is unrightful (i.e. to deprive someone of his right or to give him what is not his right), and it is prohibited. It was narrated on the authority of Thawbaan that the Prophet, sallallaahu ‘alayhi wa sallam, cursed the bribe-giver, its taker, and the one who acts as intermediary between them. [Ahmad in Al-Musnad]
If an injustice is done against a Muslim or he is entitled to a right but is unable to ward off such injustice or obtain his right except by paying money, it is allowable for him to do so, and he is not considered a bribe-giver in this situation. It is rather considered a means to ward off harm, and the one receiving the bribe from him and forcing him into giving it bears the sin for it.
The author of Tuhfat Al-Ahwathi Sharh Sunan At-Tirmithi said: “…As for what is given to obtain a right or ward off injustice, it does not fall under the category of prohibited bribery. Ibn Mas‘ood, may Allah be pleased with him, was detained in Abyssinia for some reason, and he freed himself by paying two dinars. It was also reported on the authority of a group of Taabi‘oon (followers of the Companions) that there is nothing wrong for a man to pay money to save himself or his wealth if he fears injustice.” [End of quote]
This is the ruling on bribery in general terms, but you should consult a local scholar who is better aware of the reality of transactions in your country.
Allah Knows best.