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	$153.87	8.246%	$166.5581	$166.56	$166.55	$166.60
Purchase #2	$39.59	12.610%	$44.5823	$44.58	$44.60	$44.60
Purchase #3	$233.55	9.395%	$255.492	$255.49	$255.50	$255.50
Purchase #4	$116.63	9.453%	$127.655	$127.66	$127.65	$127.70
Purchase #5	$33.71	11.382%	$37.5469	$37.55	$37.55	$37.50
Purchase #6	$37.96	10.548%	$41.964	$41.96	$41.95	$42.00
Purchase #7	$206.69	8.810%	$224.8994	$224.90	$224.90	$224.90
7 purchase totals =	$822.00		$898.6977	$898.70	$898.70	$898.80