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	$240.59	12.182%	$269.8987	$269.90	$269.90	$269.90
Purchase #2	$93.91	5.504%	$99.0788	$99.08	$99.10	$99.10
Purchase #3	$230.25	12.301%	$258.5731	$258.57	$258.55	$258.60
Purchase #4	$117.87	5.496%	$124.3481	$124.35	$124.35	$124.30
Purchase #5	$211.83	10.733%	$234.5657	$234.57	$234.55	$234.60
Purchase #6	$53.85	6.198%	$57.1876	$57.19	$57.20	$57.20
Purchase #7	$158.70	12.449%	$178.4566	$178.46	$178.45	$178.50
7 purchase totals =	$1,107.00		$1,222.1086	$1,222.12	$1,222.10	$1,222.20