Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$132.76	11.568%	$148.1177	$148.12	$148.10	$148.10
Purchase #2	$119.29	3.338%	$123.2719	$123.27	$123.25	$123.30
Purchase #3	$110.45	8.799%	$120.1685	$120.17	$120.15	$120.20
Purchase #4	$250.93	11.599%	$280.0354	$280.04	$280.05	$280.00
Purchase #5	$26.60	6.591%	$28.3532	$28.35	$28.35	$28.40
Purchase #6	$93.53	11.709%	$104.4814	$104.48	$104.50	$104.50
Purchase #7	$33.87	5.861%	$35.8551	$35.86	$35.85	$35.90
7 purchase totals =	$767.43		$840.2832	$840.29	$840.25	$840.40