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	$16.29	3.803%	$16.9095	$16.91	$16.90	$16.90
Purchase #2	$245.28	8.695%	$266.6071	$266.61	$266.60	$266.60
Purchase #3	$116.77	6.114%	$123.9093	$123.91	$123.90	$123.90
Purchase #4	$242.93	6.777%	$259.3934	$259.39	$259.40	$259.40
Purchase #5	$43.67	10.611%	$48.3038	$48.30	$48.30	$48.30
Purchase #6	$241.45	9.452%	$264.2719	$264.27	$264.25	$264.30
Purchase #7	$52.71	13.256%	$59.6972	$59.70	$59.70	$59.70
7 purchase totals =	$959.10		$1,039.0922	$1,039.09	$1,039.05	$1,039.10