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	$165.27	8.249%	$178.9031	$178.90	$178.90	$178.90
Purchase #2	$243.91	13.117%	$275.9037	$275.90	$275.90	$275.90
Purchase #3	$216.83	8.462%	$235.1782	$235.18	$235.20	$235.20
Purchase #4	$19.72	7.607%	$21.2201	$21.22	$21.20	$21.20
Purchase #5	$205.86	7.584%	$221.4724	$221.47	$221.45	$221.50
Purchase #6	$74.46	9.406%	$81.4637	$81.46	$81.45	$81.50
Purchase #7	$233.53	9.386%	$255.4491	$255.45	$255.45	$255.40
7 purchase totals =	$1,159.58		$1,269.5903	$1,269.58	$1,269.55	$1,269.60