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	$48.55	11.816%	$54.2867	$54.29	$54.30	$54.30
Purchase #2	$219.76	6.129%	$233.2291	$233.23	$233.25	$233.20
Purchase #3	$133.41	10.679%	$147.6569	$147.66	$147.65	$147.70
Purchase #4	$247.60	11.195%	$275.3188	$275.32	$275.30	$275.30
Purchase #5	$76.26	11.820%	$85.2739	$85.27	$85.25	$85.30
Purchase #6	$247.91	13.648%	$281.7448	$281.74	$281.75	$281.70
Purchase #7	$70.93	4.857%	$74.3751	$74.38	$74.40	$74.40
7 purchase totals =	$1,044.42		$1,151.8853	$1,151.89	$1,151.90	$1,151.90