Travel Money Agencies Have No Cents?

Recently, I went to exchange overseas exchange rates back into Australian currency and was told by the lady that we do not exchange cents. The issue here is something I thought would happen doesn't happen.

The excuse that I heard that they don't do that, I found to be incredible and I was left dumbfounded. The excuse was if they were to keep all the coins/cents of that currency, it would be too much to store. I'm not a person that complains but the main issue was, when I was given that currency (which was US Dollars), I was given cents/coin in US dollars and cents. So why can't I return it - that in itself is an irony.

So my question is, if they can give us the coins and we returned them for exchange back into Australia currency and we can't give them the coins, where do they originally get the coins from?

They do suggest if you don't want the coins, to donate it to charities who will exchange coins. A coin box is provided for this. Then I have the another question, who exchanges the charities coins?

I understand coins are not as big in monetary terms as dollars, but they are still legal tender.