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	$215.45	3.693%	$223.4066	$223.41	$223.40	$223.40
Purchase #2	$131.86	5.567%	$139.2006	$139.20	$139.20	$139.20
Purchase #3	$105.72	7.733%	$113.8953	$113.90	$113.90	$113.90
Purchase #4	$61.77	10.855%	$68.4751	$68.48	$68.50	$68.50
Purchase #5	$226.81	6.215%	$240.9062	$240.91	$240.90	$240.90
Purchase #6	$161.87	13.427%	$183.6043	$183.60	$183.60	$183.60
Purchase #7	$42.70	12.463%	$48.0217	$48.02	$48.00	$48.00
7 purchase totals =	$946.18		$1,017.5098	$1,017.52	$1,017.50	$1,017.50