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	$50.88	11.698%	$56.8319	$56.83	$56.85	$56.80
Purchase #2	$100.66	4.151%	$104.8384	$104.84	$104.85	$104.80
Purchase #3	$212.60	11.238%	$236.492	$236.49	$236.50	$236.50
Purchase #4	$193.82	3.443%	$200.4932	$200.49	$200.50	$200.50
Purchase #5	$210.94	8.387%	$228.6315	$228.63	$228.65	$228.60
Purchase #6	$46.64	12.422%	$52.4336	$52.43	$52.45	$52.40
Purchase #7	$234.33	3.777%	$243.1806	$243.18	$243.20	$243.20
7 purchase totals =	$1,049.87		$1,122.9012	$1,122.89	$1,123.00	$1,122.80