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	$115.89	10.766%	$128.3667	$128.37	$128.35	$128.40
Purchase #2	$106.84	7.283%	$114.6212	$114.62	$114.60	$114.60
Purchase #3	$243.87	13.782%	$277.4802	$277.48	$277.50	$277.50
Purchase #4	$97.94	12.131%	$109.8211	$109.82	$109.80	$109.80
Purchase #5	$176.65	3.349%	$182.566	$182.57	$182.55	$182.60
Purchase #6	$115.51	10.717%	$127.8892	$127.89	$127.90	$127.90
Purchase #7	$176.54	12.189%	$198.0585	$198.06	$198.05	$198.10
7 purchase totals =	$1,033.24		$1,138.8029	$1,138.81	$1,138.75	$1,138.90