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	$112.27	13.813%	$127.7779	$127.78	$127.80	$127.80
Purchase #2	$110.53	6.309%	$117.5033	$117.50	$117.50	$117.50
Purchase #3	$221.45	4.589%	$231.6123	$231.61	$231.60	$231.60
Purchase #4	$39.54	3.783%	$41.0358	$41.04	$41.05	$41.00
Purchase #5	$41.30	12.523%	$46.472	$46.47	$46.45	$46.50
Purchase #6	$209.93	11.785%	$234.6703	$234.67	$234.65	$234.70
Purchase #7	$40.44	3.389%	$41.8105	$41.81	$41.80	$41.80
7 purchase totals =	$775.46		$840.8821	$840.88	$840.85	$840.90