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	$216.85	12.753%	$244.5049	$244.50	$244.50	$244.50
Purchase #2	$93.65	12.660%	$105.5061	$105.51	$105.50	$105.50
Purchase #3	$19.87	3.184%	$20.5027	$20.50	$20.50	$20.50
Purchase #4	$70.91	8.560%	$76.9799	$76.98	$77.00	$77.00
Purchase #5	$210.96	12.730%	$237.8152	$237.82	$237.80	$237.80
Purchase #6	$124.25	3.509%	$128.6099	$128.61	$128.60	$128.60
Purchase #7	$21.72	13.664%	$24.6878	$24.69	$24.70	$24.70
7 purchase totals =	$758.21		$838.6065	$838.61	$838.60	$838.60