Round numbers are common, appealing, and easy to deal with. However they do not always end in a 0 or a 5. In fact, round numbers can take on all kinds of forms that most people would not think of. For example, a few round numbers in binary include 2, 4, 8, 1024, and 1,048,576. Most people would balk at these, but computer people feel quite comfortable with.
A number can be considered round in other ways as well. For example, a price of $9.99 is considered round because it has the same number across the board, and $123.45 is also round in that it is made up of a continuous sequence of consecutive numbers.
Numbers can also be round in terms of their geographic locations as opposed to their inherent magnitudes. For example, when entering a cooking time on a microwave, most people just enter an approximate time since there is usually no specific, to-the-second time prescribed. In this case, many people simply enter a round number such as 0:30 or 1:00. However 2:58 would also be round because it is a straight line down the middle of the numeric keypad, or 1:59 is a diagonal across the keypad. Even 1:06 is a round number if you enter it as 0:66. A time of 0:71 is round when entered as 1:11 and 83 seconds is round when entered as 1:23.
Most people think of round numbers as being evenly divisible by some factor (usually 5 or 10), but they can come in all manner of forms. They can come in handy too for example when negotiating a price for something. If you asked for $6,000 for something but they offer $5,000, instead of countering with $5,500, counter with $5,555.55. There’s a good chance they will accept and you will get a little more.