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	$235.54	3.450%	$243.6661	$243.67	$243.65	$243.70
Purchase #2	$140.54	8.773%	$152.8696	$152.87	$152.85	$152.90
Purchase #3	$158.72	9.800%	$174.2746	$174.27	$174.25	$174.30
Purchase #4	$71.79	11.366%	$79.9497	$79.95	$79.95	$79.90
Purchase #5	$142.50	4.245%	$148.5491	$148.55	$148.55	$148.50
Purchase #6	$131.37	6.182%	$139.4913	$139.49	$139.50	$139.50
Purchase #7	$11.64	7.557%	$12.5196	$12.52	$12.50	$12.50
7 purchase totals =	$892.10		$951.3200	$951.32	$951.25	$951.30