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	$54.52	9.310%	$59.5958	$59.60	$59.60	$59.60
Purchase #2	$145.52	6.151%	$154.4709	$154.47	$154.45	$154.50
Purchase #3	$84.37	12.487%	$94.9053	$94.91	$94.90	$94.90
Purchase #4	$190.46	12.496%	$214.2599	$214.26	$214.25	$214.30
Purchase #5	$74.71	8.244%	$80.8691	$80.87	$80.85	$80.90
Purchase #6	$248.55	8.358%	$269.3238	$269.32	$269.30	$269.30
Purchase #7	$83.65	8.320%	$90.6097	$90.61	$90.60	$90.60
7 purchase totals =	$881.78		$964.0345	$964.04	$963.95	$964.10