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	$47.27	11.102%	$52.5179	$52.52	$52.50	$52.50
Purchase #2	$199.64	13.451%	$226.4936	$226.49	$226.50	$226.50
Purchase #3	$67.73	7.245%	$72.637	$72.64	$72.65	$72.60
Purchase #4	$234.89	8.573%	$255.0271	$255.03	$255.05	$255.00
Purchase #5	$194.32	11.538%	$216.7406	$216.74	$216.75	$216.70
Purchase #6	$170.95	4.345%	$178.3778	$178.38	$178.40	$178.40
Purchase #7	$214.83	10.292%	$236.9403	$236.94	$236.95	$236.90
7 purchase totals =	$1,129.63		$1,238.7343	$1,238.74	$1,238.80	$1,238.60