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	$58.32	13.344%	$66.1022	$66.10	$66.10	$66.10
Purchase #2	$12.46	4.573%	$13.0298	$13.03	$13.05	$13.00
Purchase #3	$142.86	7.365%	$153.3816	$153.38	$153.40	$153.40
Purchase #4	$181.71	5.485%	$191.6768	$191.68	$191.70	$191.70
Purchase #5	$185.73	8.301%	$201.1474	$201.15	$201.15	$201.10
Purchase #6	$244.83	12.462%	$275.3407	$275.34	$275.35	$275.30
Purchase #7	$73.38	6.165%	$77.9039	$77.90	$77.90	$77.90
7 purchase totals =	$899.29		$978.5824	$978.58	$978.65	$978.50