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	$204.93	13.770%	$233.1489	$233.15	$233.15	$233.10
Purchase #2	$106.91	9.261%	$116.8109	$116.81	$116.80	$116.80
Purchase #3	$161.32	10.437%	$178.157	$178.16	$178.15	$178.20
Purchase #4	$38.47	7.625%	$41.4033	$41.40	$41.40	$41.40
Purchase #5	$64.59	10.317%	$71.2538	$71.25	$71.25	$71.30
Purchase #6	$157.68	8.380%	$170.8936	$170.89	$170.90	$170.90
Purchase #7	$133.57	4.451%	$139.5152	$139.52	$139.50	$139.50
7 purchase totals =	$867.47		$951.1827	$951.18	$951.15	$951.20