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	$10.85	13.698%	$12.3362	$12.34	$12.35	$12.30
Purchase #2	$191.69	12.670%	$215.9771	$215.98	$216.00	$216.00
Purchase #3	$219.51	9.156%	$239.6083	$239.61	$239.60	$239.60
Purchase #4	$231.41	6.259%	$245.894	$245.89	$245.90	$245.90
Purchase #5	$109.80	3.871%	$114.0504	$114.05	$114.05	$114.10
Purchase #6	$88.87	13.448%	$100.8212	$100.82	$100.80	$100.80
Purchase #7	$52.90	3.711%	$54.8631	$54.86	$54.85	$54.90
7 purchase totals =	$905.03		$983.5503	$983.55	$983.55	$983.60