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	$109.38	9.200%	$119.443	$119.44	$119.45	$119.40
Purchase #2	$229.87	12.353%	$258.2658	$258.27	$258.25	$258.30
Purchase #3	$225.91	12.343%	$253.7941	$253.79	$253.80	$253.80
Purchase #4	$46.90	8.840%	$51.046	$51.05	$51.05	$51.00
Purchase #5	$208.27	8.458%	$225.8855	$225.89	$225.90	$225.90
Purchase #6	$61.78	8.368%	$66.9498	$66.95	$66.95	$66.90
Purchase #7	$51.39	6.782%	$54.8753	$54.88	$54.90	$54.90
7 purchase totals =	$933.50		$1,030.2595	$1,030.27	$1,030.30	$1,030.20