1. Go to Defaults > Sales > Tender Type.
2. On this screen, it will have an option that says: Penniless Rounding Round to Nearest. In the field next to that, you can enter the value that ACE should round to, for example, 5 cents. Note that the cash rounding feature applies to cash payments only. Credit cards and other payment options will use the actual value of the sale. You can also change the Rounding Adjustment Name to what you prefer.
3. When you are finished, press Save.