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	$42.42	13.589%	$48.1845	$48.18	$48.20	$48.20
Purchase #2	$140.61	7.591%	$151.2837	$151.28	$151.30	$151.30
Purchase #3	$67.70	4.267%	$70.5888	$70.59	$70.60	$70.60
Purchase #4	$144.55	8.241%	$156.4624	$156.46	$156.45	$156.50
Purchase #5	$57.42	11.567%	$64.0618	$64.06	$64.05	$64.10
Purchase #6	$41.51	3.130%	$42.8093	$42.81	$42.80	$42.80
Purchase #7	$100.76	5.620%	$106.4227	$106.42	$106.40	$106.40
7 purchase totals =	$594.97		$639.8132	$639.80	$639.80	$639.90