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	$73.68	10.301%	$81.2698	$81.27	$81.25	$81.30
Purchase #2	$214.99	7.102%	$230.2586	$230.26	$230.25	$230.30
Purchase #3	$70.28	11.835%	$78.5976	$78.60	$78.60	$78.60
Purchase #4	$248.82	10.687%	$275.4114	$275.41	$275.40	$275.40
Purchase #5	$140.87	11.106%	$156.515	$156.52	$156.50	$156.50
Purchase #6	$79.42	4.677%	$83.1345	$83.13	$83.15	$83.10
Purchase #7	$21.71	9.259%	$23.7201	$23.72	$23.70	$23.70
7 purchase totals =	$849.77		$928.9070	$928.91	$928.85	$928.90