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	$91.67	9.326%	$100.2191	$100.22	$100.20	$100.20
Purchase #2	$111.41	13.379%	$126.3155	$126.32	$126.30	$126.30
Purchase #3	$52.40	12.246%	$58.8169	$58.82	$58.80	$58.80
Purchase #4	$58.91	6.213%	$62.5701	$62.57	$62.55	$62.60
Purchase #5	$122.60	4.623%	$128.2678	$128.27	$128.25	$128.30
Purchase #6	$52.74	9.447%	$57.7223	$57.72	$57.70	$57.70
Purchase #7	$70.83	13.725%	$80.5514	$80.55	$80.55	$80.60
7 purchase totals =	$560.56		$614.4631	$614.47	$614.35	$614.50