Did you ever wonder why dimes, quarters and half dollars have reeded edges while pennies and nickels do not?

The US Mint began putting reeded edges on coins containing gold and silver to discourage holders from shaving off small quantities of the precious metals. Dimes, quarters and half dollars are reeded because they used to contain silver. Pennies and nickels aren't reeded because the metals they contain are not valuable enough to shave (although with the price of copper going up, that may not be true for long)