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	$31.45	6.386%	$33.4584	$33.46	$33.45	$33.50
Purchase #2	$177.31	12.532%	$199.5305	$199.53	$199.55	$199.50
Purchase #3	$59.41	7.789%	$64.0374	$64.04	$64.05	$64.00
Purchase #4	$131.54	10.688%	$145.599	$145.60	$145.60	$145.60
Purchase #5	$36.32	11.627%	$40.5429	$40.54	$40.55	$40.50
Purchase #6	$102.64	3.500%	$106.2324	$106.23	$106.25	$106.20
Purchase #7	$231.37	12.485%	$260.2565	$260.26	$260.25	$260.30
7 purchase totals =	$770.04		$849.6571	$849.66	$849.70	$849.60