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	$54.70	9.124%	$59.6908	$59.69	$59.70	$59.70
Purchase #2	$72.89	7.851%	$78.6126	$78.61	$78.60	$78.60
Purchase #3	$11.87	7.137%	$12.7172	$12.72	$12.70	$12.70
Purchase #4	$234.45	8.281%	$253.8648	$253.86	$253.85	$253.90
Purchase #5	$54.70	9.744%	$60.03	$60.03	$60.05	$60.00
Purchase #6	$126.84	12.581%	$142.7977	$142.80	$142.80	$142.80
Purchase #7	$56.87	13.212%	$64.3837	$64.38	$64.40	$64.40
7 purchase totals =	$612.32		$672.0968	$672.09	$672.10	$672.10