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	$97.52	8.491%	$105.8004	$105.80	$105.80	$105.80
Purchase #2	$240.79	3.696%	$249.6896	$249.69	$249.70	$249.70
Purchase #3	$46.83	11.563%	$52.245	$52.25	$52.25	$52.20
Purchase #4	$145.51	7.274%	$156.0944	$156.09	$156.10	$156.10
Purchase #5	$38.60	12.455%	$43.4076	$43.41	$43.40	$43.40
Purchase #6	$54.43	11.347%	$60.6062	$60.61	$60.60	$60.60
Purchase #7	$78.76	12.681%	$88.7476	$88.75	$88.75	$88.70
7 purchase totals =	$702.44		$756.5908	$756.60	$756.60	$756.50