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	$34.59	10.296%	$38.1514	$38.15	$38.15	$38.20
Purchase #2	$131.30	12.841%	$148.1602	$148.16	$148.15	$148.20
Purchase #3	$220.72	9.348%	$241.3529	$241.35	$241.35	$241.40
Purchase #4	$134.27	8.714%	$145.9703	$145.97	$145.95	$146.00
Purchase #5	$46.70	10.463%	$51.5862	$51.59	$51.60	$51.60
Purchase #6	$12.85	3.153%	$13.2552	$13.26	$13.25	$13.30
Purchase #7	$131.57	10.837%	$145.8282	$145.83	$145.85	$145.80
7 purchase totals =	$712.00		$784.3044	$784.31	$784.30	$784.50