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	$113.88	11.587%	$127.0753	$127.08	$127.10	$127.10
Purchase #2	$56.52	6.533%	$60.2125	$60.21	$60.20	$60.20
Purchase #3	$51.88	10.395%	$57.2729	$57.27	$57.25	$57.30
Purchase #4	$67.57	7.342%	$72.531	$72.53	$72.55	$72.50
Purchase #5	$243.26	10.663%	$269.1988	$269.20	$269.20	$269.20
Purchase #6	$103.76	7.763%	$111.8149	$111.81	$111.80	$111.80
Purchase #7	$119.53	10.159%	$131.6731	$131.67	$131.65	$131.70
7 purchase totals =	$756.40		$829.7785	$829.77	$829.75	$829.80