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	$174.27	6.244%	$185.1514	$185.15	$185.15	$185.20
Purchase #2	$71.64	13.178%	$81.0807	$81.08	$81.10	$81.10
Purchase #3	$199.93	11.430%	$222.782	$222.78	$222.80	$222.80
Purchase #4	$88.47	13.701%	$100.5913	$100.59	$100.60	$100.60
Purchase #5	$104.82	11.408%	$116.7779	$116.78	$116.80	$116.80
Purchase #6	$89.53	10.737%	$99.1428	$99.14	$99.15	$99.10
Purchase #7	$169.91	4.191%	$177.0309	$177.03	$177.05	$177.00
7 purchase totals =	$898.57		$982.5570	$982.55	$982.65	$982.60