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	$223.67	12.659%	$251.9844	$251.98	$252.00	$252.00
Purchase #2	$34.57	13.367%	$39.191	$39.19	$39.20	$39.20
Purchase #3	$212.38	5.214%	$223.4535	$223.45	$223.45	$223.50
Purchase #4	$40.47	6.619%	$43.1487	$43.15	$43.15	$43.10
Purchase #5	$237.89	13.677%	$270.4262	$270.43	$270.45	$270.40
Purchase #6	$59.63	10.826%	$66.0855	$66.09	$66.10	$66.10
Purchase #7	$35.48	7.294%	$38.0679	$38.07	$38.05	$38.10
7 purchase totals =	$844.09		$932.3572	$932.36	$932.40	$932.40