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	$145.87	13.713%	$165.8732	$165.87	$165.85	$165.90
Purchase #2	$72.69	11.162%	$80.8037	$80.80	$80.80	$80.80
Purchase #3	$129.34	11.235%	$143.8713	$143.87	$143.85	$143.90
Purchase #4	$44.25	4.869%	$46.4045	$46.40	$46.40	$46.40
Purchase #5	$184.52	7.680%	$198.6911	$198.69	$198.70	$198.70
Purchase #6	$157.54	12.205%	$176.7678	$176.77	$176.75	$176.80
Purchase #7	$18.86	10.760%	$20.8893	$20.89	$20.90	$20.90
7 purchase totals =	$753.07		$833.3009	$833.29	$833.25	$833.40