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	$30.82	7.226%	$33.0471	$33.05	$33.05	$33.00
Purchase #2	$48.64	7.321%	$52.2009	$52.20	$52.20	$52.20
Purchase #3	$30.49	12.504%	$34.3025	$34.30	$34.30	$34.30
Purchase #4	$230.71	10.295%	$254.4616	$254.46	$254.45	$254.50
Purchase #5	$41.25	3.253%	$42.5919	$42.59	$42.60	$42.60
Purchase #6	$21.53	10.528%	$23.7967	$23.80	$23.80	$23.80
Purchase #7	$56.50	8.829%	$61.4884	$61.49	$61.50	$61.50
7 purchase totals =	$459.94		$501.8891	$501.89	$501.90	$501.90