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	$19.98	9.831%	$21.9442	$21.94	$21.95	$21.90
Purchase #2	$113.72	8.568%	$123.4635	$123.46	$123.45	$123.50
Purchase #3	$30.59	11.258%	$34.0338	$34.03	$34.05	$34.00
Purchase #4	$53.80	10.753%	$59.5851	$59.59	$59.60	$59.60
Purchase #5	$214.56	5.131%	$225.5691	$225.57	$225.55	$225.60
Purchase #6	$194.79	8.212%	$210.7862	$210.79	$210.80	$210.80
Purchase #7	$199.71	7.514%	$214.7162	$214.72	$214.70	$214.70
7 purchase totals =	$827.15		$890.0981	$890.10	$890.10	$890.10