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	$99.70	12.126%	$111.7896	$111.79	$111.80	$111.80
Purchase #2	$123.96	3.208%	$127.9366	$127.94	$127.95	$127.90
Purchase #3	$139.70	4.191%	$145.5548	$145.55	$145.55	$145.60
Purchase #4	$126.77	8.600%	$137.6722	$137.67	$137.65	$137.70
Purchase #5	$45.76	6.802%	$48.8726	$48.87	$48.85	$48.90
Purchase #6	$201.96	5.722%	$213.5162	$213.52	$213.50	$213.50
Purchase #7	$47.84	3.589%	$49.557	$49.56	$49.55	$49.60
7 purchase totals =	$785.69		$834.8990	$834.90	$834.85	$835.00