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	$160.58	3.698%	$166.5182	$166.52	$166.50	$166.50
Purchase #2	$34.51	11.209%	$38.3782	$38.38	$38.40	$38.40
Purchase #3	$36.49	11.343%	$40.6291	$40.63	$40.65	$40.60
Purchase #4	$6.73	12.199%	$7.551	$7.55	$7.55	$7.60
Purchase #5	$244.80	4.462%	$255.723	$255.72	$255.70	$255.70
Purchase #6	$62.67	12.286%	$70.3696	$70.37	$70.35	$70.40
Purchase #7	$84.41	10.526%	$93.295	$93.30	$93.30	$93.30
7 purchase totals =	$630.19		$672.4641	$672.47	$672.45	$672.50