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	$247.51	3.422%	$255.9798	$255.98	$256.00	$256.00
Purchase #2	$60.70	12.331%	$68.1849	$68.18	$68.20	$68.20
Purchase #3	$201.88	11.849%	$225.8008	$225.80	$225.80	$225.80
Purchase #4	$112.89	12.807%	$127.3478	$127.35	$127.35	$127.30
Purchase #5	$154.77	5.275%	$162.9341	$162.93	$162.95	$162.90
Purchase #6	$172.84	10.253%	$190.5613	$190.56	$190.55	$190.60
Purchase #7	$170.30	6.634%	$181.5977	$181.60	$181.60	$181.60
7 purchase totals =	$1,120.89		$1,212.4064	$1,212.40	$1,212.45	$1,212.40