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	$58.98	6.819%	$63.0018	$63.00	$63.00	$63.00
Purchase #2	$177.75	12.860%	$200.6087	$200.61	$200.60	$200.60
Purchase #3	$84.72	5.662%	$89.5168	$89.52	$89.50	$89.50
Purchase #4	$118.74	4.229%	$123.7615	$123.76	$123.75	$123.80
Purchase #5	$70.41	4.864%	$73.8347	$73.83	$73.85	$73.80
Purchase #6	$39.59	11.358%	$44.0866	$44.09	$44.10	$44.10
Purchase #7	$105.51	10.568%	$116.6603	$116.66	$116.65	$116.70
7 purchase totals =	$655.70		$711.4704	$711.47	$711.45	$711.50