At Accra trotro terminals or makeshift stops, you can obtain change. The trader will sell the coins to you at a fee so you give them One Ghana Cedi and they give you 90 Pesewas. The 10 Pesewas become their profit because they have to source the coins to make them available to you. You can also obtain coins from the bank. Bring change along with you to the terminal.
You can also buy something and get change in return. Its rare for a trader to dispense with so much change during early morning. If you hold out any money to buy, ensure that your change is not more than 25% of your note else you may be ignored. For example, you can buy a 3 Cedis loaf of bread with a 5 Cedi note. It will be a futile idea to try to buy a 2 Cedis loaf of bread with a 20 Ghana cedi. Its ostensible you are looking for change and you will not be entertained.