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	$66.94	9.748%	$73.4653	$73.47	$73.45	$73.50
Purchase #2	$73.33	12.654%	$82.6092	$82.61	$82.60	$82.60
Purchase #3	$48.32	4.581%	$50.5335	$50.53	$50.55	$50.50
Purchase #4	$215.77	4.119%	$224.6576	$224.66	$224.65	$224.70
Purchase #5	$158.31	9.830%	$173.8719	$173.87	$173.85	$173.90
Purchase #6	$117.71	6.127%	$124.9221	$124.92	$124.90	$124.90
Purchase #7	$146.98	8.340%	$159.2381	$159.24	$159.25	$159.20
7 purchase totals =	$827.36		$889.2977	$889.30	$889.25	$889.30