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	$155.63	6.197%	$165.2744	$165.27	$165.25	$165.30
Purchase #2	$199.80	7.628%	$215.0407	$215.04	$215.05	$215.00
Purchase #3	$247.52	11.813%	$276.7595	$276.76	$276.75	$276.80
Purchase #4	$140.85	4.378%	$147.0164	$147.02	$147.00	$147.00
Purchase #5	$67.54	4.343%	$70.4733	$70.47	$70.45	$70.50
Purchase #6	$137.76	12.146%	$154.4923	$154.49	$154.50	$154.50
Purchase #7	$67.93	3.792%	$70.5059	$70.51	$70.50	$70.50
7 purchase totals =	$1,017.03		$1,099.5625	$1,099.56	$1,099.50	$1,099.60