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	$105.47	5.487%	$111.2571	$111.26	$111.25	$111.30
Purchase #2	$39.94	6.333%	$42.4694	$42.47	$42.45	$42.50
Purchase #3	$146.72	6.443%	$156.1732	$156.17	$156.15	$156.20
Purchase #4	$213.52	12.251%	$239.6783	$239.68	$239.70	$239.70
Purchase #5	$188.88	9.383%	$206.6026	$206.60	$206.60	$206.60
Purchase #6	$132.25	10.125%	$145.6403	$145.64	$145.65	$145.60
Purchase #7	$72.75	10.583%	$80.4491	$80.45	$80.45	$80.40
7 purchase totals =	$899.53		$982.2700	$982.27	$982.25	$982.30