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	$126.57	6.473%	$134.7629	$134.76	$134.75	$134.80
Purchase #2	$240.81	7.347%	$258.5023	$258.50	$258.50	$258.50
Purchase #3	$64.66	9.214%	$70.6178	$70.62	$70.60	$70.60
Purchase #4	$86.71	4.447%	$90.566	$90.57	$90.55	$90.60
Purchase #5	$112.74	10.439%	$124.5089	$124.51	$124.50	$124.50
Purchase #6	$35.82	7.688%	$38.5738	$38.57	$38.55	$38.60
Purchase #7	$133.59	6.376%	$142.1077	$142.11	$142.10	$142.10
7 purchase totals =	$800.90		$859.6394	$859.64	$859.55	$859.70