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	$131.87	11.336%	$146.8188	$146.82	$146.80	$146.80
Purchase #2	$28.89	13.267%	$32.7228	$32.72	$32.70	$32.70
Purchase #3	$74.31	12.150%	$83.3387	$83.34	$83.35	$83.30
Purchase #4	$19.46	9.808%	$21.3686	$21.37	$21.35	$21.40
Purchase #5	$222.90	10.455%	$246.2042	$246.20	$246.20	$246.20
Purchase #6	$130.51	11.567%	$145.6061	$145.61	$145.60	$145.60
Purchase #7	$108.27	4.124%	$112.7351	$112.74	$112.75	$112.70
7 purchase totals =	$716.21		$788.7943	$788.80	$788.75	$788.70