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	$155.86	6.418%	$165.8631	$165.86	$165.85	$165.90
Purchase #2	$99.58	10.772%	$110.3068	$110.31	$110.30	$110.30
Purchase #3	$126.85	13.222%	$143.6221	$143.62	$143.60	$143.60
Purchase #4	$147.41	13.866%	$167.8499	$167.85	$167.85	$167.80
Purchase #5	$38.55	6.699%	$41.1325	$41.13	$41.15	$41.10
Purchase #6	$146.61	8.238%	$158.6877	$158.69	$158.70	$158.70
Purchase #7	$136.32	8.131%	$147.4042	$147.40	$147.40	$147.40
7 purchase totals =	$851.18		$934.8663	$934.86	$934.85	$934.80