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	$74.74	4.492%	$78.0973	$78.10	$78.10	$78.10
Purchase #2	$18.97	12.438%	$21.3295	$21.33	$21.35	$21.30
Purchase #3	$69.82	11.129%	$77.5903	$77.59	$77.60	$77.60
Purchase #4	$79.83	7.300%	$85.6576	$85.66	$85.65	$85.70
Purchase #5	$60.81	3.278%	$62.8034	$62.80	$62.80	$62.80
Purchase #6	$87.52	10.468%	$96.6816	$96.68	$96.70	$96.70
Purchase #7	$191.94	13.342%	$217.5486	$217.55	$217.55	$217.50
7 purchase totals =	$583.63		$639.7083	$639.71	$639.75	$639.70