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	$223.98	13.854%	$255.0102	$255.01	$255.00	$255.00
Purchase #2	$8.71	12.804%	$9.8252	$9.83	$9.85	$9.80
Purchase #3	$158.89	12.737%	$179.1278	$179.13	$179.15	$179.10
Purchase #4	$62.69	5.533%	$66.1586	$66.16	$66.15	$66.20
Purchase #5	$53.57	8.151%	$57.9365	$57.94	$57.95	$57.90
Purchase #6	$139.51	13.667%	$158.5768	$158.58	$158.60	$158.60
Purchase #7	$139.30	5.215%	$146.5645	$146.56	$146.55	$146.60
7 purchase totals =	$786.65		$873.1996	$873.21	$873.25	$873.20