Accepting a different currency from a customer and exchanging it for a better rate later on

I work at the airport at a car rental. Now if a customer comes and wants to pay in Euros but we accept only Dinars, to make his work easy I take the Euros from him at the current exchange rate at the airport knowing that the exchange rate will be better outside in the city. So I accept those Euros and use my Dinars to give to the company and later take those Euros and exchange it in the market at a better rate for myself or sometimes I wait for an even better rate. Is this money halaal?