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	$11.74	11.495%	$13.0895	$13.09	$13.10	$13.10
Purchase #2	$145.45	6.355%	$154.6933	$154.69	$154.70	$154.70
Purchase #3	$209.40	7.123%	$224.3156	$224.32	$224.30	$224.30
Purchase #4	$95.56	5.404%	$100.7241	$100.72	$100.70	$100.70
Purchase #5	$159.66	13.184%	$180.7096	$180.71	$180.70	$180.70
Purchase #6	$95.72	13.232%	$108.3857	$108.39	$108.40	$108.40
Purchase #7	$240.75	10.300%	$265.5473	$265.55	$265.55	$265.50
7 purchase totals =	$958.28		$1,047.4651	$1,047.47	$1,047.45	$1,047.40