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	$82.83	12.710%	$93.3577	$93.36	$93.35	$93.40
Purchase #2	$99.77	5.710%	$105.4669	$105.47	$105.45	$105.50
Purchase #3	$204.34	11.237%	$227.3017	$227.30	$227.30	$227.30
Purchase #4	$129.70	9.753%	$142.3496	$142.35	$142.35	$142.30
Purchase #5	$111.70	10.517%	$123.4475	$123.45	$123.45	$123.40
Purchase #6	$113.93	8.124%	$123.1857	$123.19	$123.20	$123.20
Purchase #7	$198.25	3.763%	$205.7101	$205.71	$205.70	$205.70
7 purchase totals =	$940.52		$1,020.8192	$1,020.83	$1,020.80	$1,020.80