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	$192.28	13.332%	$217.9148	$217.91	$217.90	$217.90
Purchase #2	$114.80	3.322%	$118.6137	$118.61	$118.60	$118.60
Purchase #3	$76.83	11.196%	$85.4319	$85.43	$85.45	$85.40
Purchase #4	$225.75	13.390%	$255.9779	$255.98	$256.00	$256.00
Purchase #5	$228.72	13.686%	$260.0226	$260.02	$260.00	$260.00
Purchase #6	$142.65	4.323%	$148.8168	$148.82	$148.80	$148.80
Purchase #7	$36.69	12.197%	$41.1651	$41.17	$41.15	$41.20
7 purchase totals =	$1,017.72		$1,127.9428	$1,127.94	$1,127.90	$1,127.90