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	$138.46	4.308%	$144.4249	$144.42	$144.40	$144.40
Purchase #2	$245.54	8.133%	$265.5098	$265.51	$265.50	$265.50
Purchase #3	$221.38	11.785%	$247.4696	$247.47	$247.45	$247.50
Purchase #4	$208.44	4.817%	$218.4806	$218.48	$218.50	$218.50
Purchase #5	$10.46	13.297%	$11.8509	$11.85	$11.85	$11.90
Purchase #6	$234.96	10.165%	$258.8437	$258.84	$258.85	$258.80
Purchase #7	$39.84	6.397%	$42.3886	$42.39	$42.40	$42.40
7 purchase totals =	$1,099.08		$1,188.9681	$1,188.96	$1,188.95	$1,189.00