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	$236.25	4.647%	$247.2285	$247.23	$247.25	$247.20
Purchase #2	$165.56	4.269%	$172.6278	$172.63	$172.65	$172.60
Purchase #3	$197.71	12.744%	$222.9062	$222.91	$222.90	$222.90
Purchase #4	$195.89	13.584%	$222.4997	$222.50	$222.50	$222.50
Purchase #5	$131.39	10.453%	$145.1242	$145.12	$145.10	$145.10
Purchase #6	$74.67	3.259%	$77.1035	$77.10	$77.10	$77.10
Purchase #7	$71.78	9.156%	$78.3522	$78.35	$78.35	$78.40
7 purchase totals =	$1,073.25		$1,165.8421	$1,165.84	$1,165.85	$1,165.80