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	$72.56	7.871%	$78.2712	$78.27	$78.25	$78.30
Purchase #2	$222.69	5.389%	$234.6908	$234.69	$234.70	$234.70
Purchase #3	$226.60	10.271%	$249.8741	$249.87	$249.85	$249.90
Purchase #4	$228.92	10.708%	$253.4328	$253.43	$253.45	$253.40
Purchase #5	$50.43	8.837%	$54.8865	$54.89	$54.90	$54.90
Purchase #6	$165.81	7.218%	$177.7782	$177.78	$177.80	$177.80
Purchase #7	$149.84	13.105%	$169.4765	$169.48	$169.50	$169.50
7 purchase totals =	$1,116.85		$1,218.4101	$1,218.41	$1,218.45	$1,218.50