Funny transaction

Youngest clerk of a large company had at a certain occasion lent three dollars from the accountant. By a former occasion the accountant had lent on his turn two dollars from the cashier. And when the cashier was stuck with the paying on certain day, he had lent two dollars from the youngest clerk.

On a good day the youngest clerk found a dollar on the street. He gave it immediately to the accountant, as a redemption to his debt that with this was decreased to only two dollars. The accountant gave that dollar along to the cashier and said: 'Now I owe you one dollar'.
The same said the cashier to the youngest clerk, while he handed him the dollar. Then the clerk went back to the accountant, gave him the dollar and said: 'Now I owe you only one dollar.'
The accountant gave the dollar straight to the cashier, with the words: 'Now we're even.'
'Now we're are even,' said also the cashier to the clerk, while he laid him the dollar in his hand.
Immediately the clerk walked to the accountant, to give him a dollar for the third time, and said: 'Now we're even.'

With one dollar three debts were paid, while together they owed 7 dollars. What happened mathematically?