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	$51.67	8.744%	$56.188	$56.19	$56.20	$56.20
Purchase #2	$111.87	3.542%	$115.8324	$115.83	$115.85	$115.80
Purchase #3	$158.73	3.602%	$164.4475	$164.45	$164.45	$164.40
Purchase #4	$143.78	5.392%	$151.5326	$151.53	$151.55	$151.50
Purchase #5	$69.77	12.737%	$78.6566	$78.66	$78.65	$78.70
Purchase #6	$100.97	7.212%	$108.252	$108.25	$108.25	$108.30
Purchase #7	$78.40	4.834%	$82.1899	$82.19	$82.20	$82.20
7 purchase totals =	$715.19		$757.0990	$757.10	$757.15	$757.10