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	$79.84	3.547%	$82.6719	$82.67	$82.65	$82.70
Purchase #2	$143.39	9.331%	$156.7697	$156.77	$156.75	$156.80
Purchase #3	$154.85	11.210%	$172.2087	$172.21	$172.20	$172.20
Purchase #4	$34.83	9.294%	$38.0671	$38.07	$38.05	$38.10
Purchase #5	$170.60	5.273%	$179.5957	$179.60	$179.60	$179.60
Purchase #6	$199.90	11.129%	$222.1469	$222.15	$222.15	$222.10
Purchase #7	$225.41	11.552%	$251.4494	$251.45	$251.45	$251.40
7 purchase totals =	$1,008.82		$1,102.9094	$1,102.92	$1,102.85	$1,102.90