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	$69.77	4.395%	$72.8364	$72.84	$72.85	$72.80
Purchase #2	$172.51	12.701%	$194.4205	$194.42	$194.40	$194.40
Purchase #3	$34.34	7.307%	$36.8492	$36.85	$36.85	$36.80
Purchase #4	$133.78	6.312%	$142.2242	$142.22	$142.20	$142.20
Purchase #5	$228.46	8.753%	$248.4571	$248.46	$248.45	$248.50
Purchase #6	$232.82	9.775%	$255.5782	$255.58	$255.60	$255.60
Purchase #7	$188.75	5.848%	$199.7881	$199.79	$199.80	$199.80
7 purchase totals =	$1,060.43		$1,150.1537	$1,150.16	$1,150.15	$1,150.10