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	$113.72	12.583%	$128.0294	$128.03	$128.05	$128.00
Purchase #2	$104.47	6.336%	$111.0892	$111.09	$111.10	$111.10
Purchase #3	$35.51	12.145%	$39.8227	$39.82	$39.80	$39.80
Purchase #4	$104.84	8.841%	$114.1089	$114.11	$114.10	$114.10
Purchase #5	$206.45	11.509%	$230.2103	$230.21	$230.20	$230.20
Purchase #6	$99.34	11.874%	$111.1356	$111.14	$111.15	$111.10
Purchase #7	$66.92	12.730%	$75.4389	$75.44	$75.45	$75.40
7 purchase totals =	$731.25		$809.8350	$809.84	$809.85	$809.70