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	$237.85	7.634%	$256.0075	$256.01	$256.00	$256.00
Purchase #2	$59.80	10.429%	$66.0365	$66.04	$66.05	$66.00
Purchase #3	$222.42	6.216%	$236.2456	$236.25	$236.25	$236.20
Purchase #4	$47.75	11.836%	$53.4017	$53.40	$53.40	$53.40
Purchase #5	$46.88	13.688%	$53.2969	$53.30	$53.30	$53.30
Purchase #6	$172.55	13.746%	$196.2687	$196.27	$196.25	$196.30
Purchase #7	$73.47	4.249%	$76.5917	$76.59	$76.60	$76.60
7 purchase totals =	$860.72		$937.8486	$937.86	$937.85	$937.80