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	$122.45	4.574%	$128.0509	$128.05	$128.05	$128.10
Purchase #2	$148.83	6.408%	$158.367	$158.37	$158.35	$158.40
Purchase #3	$183.42	4.396%	$191.4831	$191.48	$191.50	$191.50
Purchase #4	$136.35	7.198%	$146.1645	$146.16	$146.15	$146.20
Purchase #5	$11.50	10.757%	$12.7371	$12.74	$12.75	$12.70
Purchase #6	$176.52	13.159%	$199.7483	$199.75	$199.75	$199.70
Purchase #7	$100.68	10.481%	$111.2323	$111.23	$111.25	$111.20
7 purchase totals =	$879.75		$947.7832	$947.78	$947.80	$947.80