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	$165.54	4.263%	$172.597	$172.60	$172.60	$172.60
Purchase #2	$242.72	8.708%	$263.8561	$263.86	$263.85	$263.90
Purchase #3	$169.32	6.570%	$180.4443	$180.44	$180.45	$180.40
Purchase #4	$73.49	5.726%	$77.698	$77.70	$77.70	$77.70
Purchase #5	$115.83	11.526%	$129.1806	$129.18	$129.20	$129.20
Purchase #6	$246.95	3.466%	$255.5093	$255.51	$255.50	$255.50
Purchase #7	$11.58	5.357%	$12.2003	$12.20	$12.20	$12.20
7 purchase totals =	$1,025.43		$1,091.4856	$1,091.49	$1,091.50	$1,091.50