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	$130.54	10.633%	$144.4203	$144.42	$144.40	$144.40
Purchase #2	$50.98	7.629%	$54.8693	$54.87	$54.85	$54.90
Purchase #3	$237.52	6.420%	$252.7688	$252.77	$252.75	$252.80
Purchase #4	$100.87	4.571%	$105.4808	$105.48	$105.50	$105.50
Purchase #5	$75.88	5.450%	$80.0155	$80.02	$80.00	$80.00
Purchase #6	$102.57	10.772%	$113.6188	$113.62	$113.60	$113.60
Purchase #7	$46.45	3.680%	$48.1594	$48.16	$48.15	$48.20
7 purchase totals =	$744.81		$799.3329	$799.34	$799.25	$799.40