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	$180.29	6.378%	$191.7889	$191.79	$191.80	$191.80
Purchase #2	$228.97	10.836%	$253.7812	$253.78	$253.80	$253.80
Purchase #3	$247.90	5.727%	$262.0972	$262.10	$262.10	$262.10
Purchase #4	$127.52	8.599%	$138.4854	$138.49	$138.50	$138.50
Purchase #5	$11.30	10.772%	$12.5172	$12.52	$12.50	$12.50
Purchase #6	$60.94	12.691%	$68.6739	$68.67	$68.65	$68.70
Purchase #7	$72.80	7.859%	$78.5214	$78.52	$78.50	$78.50
7 purchase totals =	$929.72		$1,005.8652	$1,005.87	$1,005.85	$1,005.90