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	$235.37	9.112%	$256.8169	$256.82	$256.80	$256.80
Purchase #2	$236.75	11.857%	$264.8214	$264.82	$264.80	$264.80
Purchase #3	$18.45	3.515%	$19.0985	$19.10	$19.10	$19.10
Purchase #4	$54.72	10.684%	$60.5663	$60.57	$60.55	$60.60
Purchase #5	$245.63	5.316%	$258.6877	$258.69	$258.70	$258.70
Purchase #6	$248.67	13.855%	$283.1232	$283.12	$283.10	$283.10
Purchase #7	$179.69	9.313%	$196.4245	$196.42	$196.40	$196.40
7 purchase totals =	$1,219.28		$1,339.5385	$1,339.54	$1,339.45	$1,339.50