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	$94.36	5.764%	$99.7989	$99.80	$99.80	$99.80
Purchase #2	$108.89	11.322%	$121.2185	$121.22	$121.20	$121.20
Purchase #3	$88.70	9.848%	$97.4352	$97.44	$97.45	$97.40
Purchase #4	$199.38	9.246%	$217.8147	$217.81	$217.80	$217.80
Purchase #5	$151.89	13.330%	$172.1369	$172.14	$172.15	$172.10
Purchase #6	$120.91	5.767%	$127.8829	$127.88	$127.90	$127.90
Purchase #7	$136.28	5.305%	$143.5097	$143.51	$143.50	$143.50
7 purchase totals =	$900.41		$979.7968	$979.80	$979.80	$979.70