Practice counting by fives, 10s, 20s and 25s with your child. Most coinage and bills around the world are divided in this manner, so having a firm grasp of such counting will make it easier for your child to count his money.
Purchase fake money from the dollar or toy store and count it with your child, making sure he understands which coins represent which amount of money. Put it into practice by setting up a "shop" with your child. Mark items, such as food or toys, with a price and ask him to "buy" it from you using the appropriate amount of money. When your child has mastered that, let him be the merchant and "buy" items from him, asking him to give you correct change.
Play board games that incorporate money into them, such as a children's version of Monopoly. This will enable the child to use fake money in an applied situation.
Take your child with you when you purchase items in cash so she can watch you count the money. Count out loud so she can understand what you are doing. Once your child has gained the skills necessary to count money, give her cash and let her pay for items.