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	$85.62	4.412%	$89.3976	$89.40	$89.40	$89.40
Purchase #2	$58.61	5.460%	$61.8101	$61.81	$61.80	$61.80
Purchase #3	$218.98	7.585%	$235.5896	$235.59	$235.60	$235.60
Purchase #4	$83.46	8.762%	$90.7728	$90.77	$90.75	$90.80
Purchase #5	$227.91	13.423%	$258.5024	$258.50	$258.50	$258.50
Purchase #6	$55.65	7.437%	$59.7887	$59.79	$59.80	$59.80
Purchase #7	$83.79	8.318%	$90.7597	$90.76	$90.75	$90.80
7 purchase totals =	$814.02		$886.6209	$886.62	$886.60	$886.70