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	$109.47	11.668%	$122.243	$122.24	$122.25	$122.20
Purchase #2	$163.83	5.176%	$172.3098	$172.31	$172.30	$172.30
Purchase #3	$246.61	3.662%	$255.6409	$255.64	$255.65	$255.60
Purchase #4	$36.50	13.702%	$41.5012	$41.50	$41.50	$41.50
Purchase #5	$197.42	6.282%	$209.8219	$209.82	$209.80	$209.80
Purchase #6	$49.85	5.375%	$52.5294	$52.53	$52.55	$52.50
Purchase #7	$16.89	13.240%	$19.1262	$19.13	$19.15	$19.10
7 purchase totals =	$820.57		$873.1724	$873.17	$873.20	$873.00