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	$99.47	12.482%	$111.8858	$111.89	$111.90	$111.90
Purchase #2	$87.34	8.221%	$94.5202	$94.52	$94.50	$94.50
Purchase #3	$248.81	6.695%	$265.4678	$265.47	$265.45	$265.50
Purchase #4	$220.78	11.422%	$245.9975	$246.00	$246.00	$246.00
Purchase #5	$139.59	4.709%	$146.1633	$146.16	$146.15	$146.20
Purchase #6	$36.33	11.782%	$40.6104	$40.61	$40.60	$40.60
Purchase #7	$239.65	9.686%	$262.8625	$262.86	$262.85	$262.90
7 purchase totals =	$1,071.97		$1,167.5075	$1,167.51	$1,167.45	$1,167.60