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	$54.48	5.743%	$57.6088	$57.61	$57.60	$57.60
Purchase #2	$126.35	10.239%	$139.287	$139.29	$139.30	$139.30
Purchase #3	$54.85	13.180%	$62.0792	$62.08	$62.10	$62.10
Purchase #4	$61.48	7.592%	$66.1476	$66.15	$66.15	$66.10
Purchase #5	$53.90	13.557%	$61.2072	$61.21	$61.20	$61.20
Purchase #6	$10.27	9.102%	$11.2048	$11.20	$11.20	$11.20
Purchase #7	$102.40	9.298%	$111.9212	$111.92	$111.90	$111.90
7 purchase totals =	$463.73		$509.4558	$509.46	$509.45	$509.40