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	$173.59	10.386%	$191.6191	$191.62	$191.60	$191.60
Purchase #2	$14.25	13.854%	$16.2242	$16.22	$16.20	$16.20
Purchase #3	$140.42	11.424%	$156.4616	$156.46	$156.45	$156.50
Purchase #4	$227.45	10.426%	$251.1639	$251.16	$251.15	$251.20
Purchase #5	$11.71	6.468%	$12.4674	$12.47	$12.45	$12.50
Purchase #6	$55.82	9.318%	$61.0213	$61.02	$61.00	$61.00
Purchase #7	$133.33	4.628%	$139.5005	$139.50	$139.50	$139.50
7 purchase totals =	$756.57		$828.4580	$828.45	$828.35	$828.50