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	$102.71	3.587%	$106.3942	$106.39	$106.40	$106.40
Purchase #2	$54.67	8.612%	$59.3782	$59.38	$59.40	$59.40
Purchase #3	$232.64	8.706%	$252.8936	$252.89	$252.90	$252.90
Purchase #4	$154.95	12.825%	$174.8223	$174.82	$174.80	$174.80
Purchase #5	$31.85	5.462%	$33.5896	$33.59	$33.60	$33.60
Purchase #6	$71.47	10.668%	$79.0944	$79.09	$79.10	$79.10
Purchase #7	$115.93	6.830%	$123.848	$123.85	$123.85	$123.80
7 purchase totals =	$764.22		$830.0203	$830.01	$830.05	$830.00