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	$225.68	13.400%	$255.9211	$255.92	$255.90	$255.90
Purchase #2	$139.45	12.178%	$156.4322	$156.43	$156.45	$156.40
Purchase #3	$14.69	7.532%	$15.7965	$15.80	$15.80	$15.80
Purchase #4	$173.60	9.463%	$190.0278	$190.03	$190.05	$190.00
Purchase #5	$175.49	7.332%	$188.3569	$188.36	$188.35	$188.40
Purchase #6	$51.76	3.291%	$53.4634	$53.46	$53.45	$53.50
Purchase #7	$90.81	8.525%	$98.5516	$98.55	$98.55	$98.60
7 purchase totals =	$871.48		$958.5495	$958.55	$958.55	$958.60