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	$198.50	11.482%	$221.2918	$221.29	$221.30	$221.30
Purchase #2	$42.90	8.191%	$46.4139	$46.41	$46.40	$46.40
Purchase #3	$106.82	4.792%	$111.9388	$111.94	$111.95	$111.90
Purchase #4	$122.89	12.710%	$138.5093	$138.51	$138.50	$138.50
Purchase #5	$149.38	13.682%	$169.8182	$169.82	$169.80	$169.80
Purchase #6	$193.96	10.310%	$213.9573	$213.96	$213.95	$214.00
Purchase #7	$84.51	6.184%	$89.7361	$89.74	$89.75	$89.70
7 purchase totals =	$898.96		$991.6654	$991.67	$991.65	$991.60