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	$100.83	6.605%	$107.4898	$107.49	$107.50	$107.50
Purchase #2	$116.85	12.792%	$131.7975	$131.80	$131.80	$131.80
Purchase #3	$190.39	13.263%	$215.6414	$215.64	$215.65	$215.60
Purchase #4	$20.72	5.548%	$21.8695	$21.87	$21.85	$21.90
Purchase #5	$77.79	7.414%	$83.5574	$83.56	$83.55	$83.60
Purchase #6	$208.31	8.244%	$225.4831	$225.48	$225.50	$225.50
Purchase #7	$173.94	11.229%	$193.4717	$193.47	$193.45	$193.50
7 purchase totals =	$888.83		$979.3104	$979.31	$979.30	$979.40