is it a form of Corruption?

i work in a government office and i am a newly hired employee...i was asked by my boss to purchased 6 reams of mimeo papers then i did so.. i was given 1000php to buy the said items.. then i find a store where i can buy the items in cheaper amount... then when i found one... the store owner told me that the item cost 155php per reams which means i could only buy 6 reams.. that would total to 930php.. then i told the store owner that im gonna ask for official receipt then name it the government office that i work with then i ask for discounts if there is.. then the store owner gave me 5 percent discount.. then the next thing is after the official receipt has been given to me i tried to check the official receipt then i noticed something that the store owner didn't give me a discount.. so i asked the owner what happen to the discount.. the owner told me that the discount won't appear in the official receipt and the that amount ill be paying is 883.5php instead of of 930php.. so i paid the store owner and was given a change over my 1000php bill... i now have 46.50php money from a government fund..