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	$34.64	7.534%	$37.2498	$37.25	$37.25	$37.20
Purchase #2	$136.52	10.233%	$150.4901	$150.49	$150.50	$150.50
Purchase #3	$235.74	13.181%	$266.8129	$266.81	$266.80	$266.80
Purchase #4	$47.78	13.495%	$54.2279	$54.23	$54.25	$54.20
Purchase #5	$41.75	4.427%	$43.5983	$43.60	$43.60	$43.60
Purchase #6	$35.38	4.743%	$37.0581	$37.06	$37.05	$37.10
Purchase #7	$214.76	8.108%	$232.1727	$232.17	$232.15	$232.20
7 purchase totals =	$746.57		$821.6098	$821.61	$821.60	$821.60