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	$245.31	4.479%	$256.2974	$256.30	$256.30	$256.30
Purchase #2	$59.50	12.863%	$67.1535	$67.15	$67.15	$67.20
Purchase #3	$94.79	10.800%	$105.0273	$105.03	$105.05	$105.00
Purchase #4	$100.90	5.643%	$106.5938	$106.59	$106.60	$106.60
Purchase #5	$141.63	4.490%	$147.9892	$147.99	$148.00	$148.00
Purchase #6	$10.90	4.663%	$11.4083	$11.41	$11.40	$11.40
Purchase #7	$116.89	10.162%	$128.7684	$128.77	$128.75	$128.80
7 purchase totals =	$769.92		$823.2379	$823.24	$823.25	$823.30