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	$40.34	3.239%	$41.6466	$41.65	$41.65	$41.60
Purchase #2	$42.75	8.719%	$46.4774	$46.48	$46.50	$46.50
Purchase #3	$165.43	4.742%	$173.2747	$173.27	$173.25	$173.30
Purchase #4	$132.48	5.221%	$139.3968	$139.40	$139.40	$139.40
Purchase #5	$34.60	6.123%	$36.7186	$36.72	$36.70	$36.70
Purchase #6	$140.81	3.393%	$145.5877	$145.59	$145.60	$145.60
Purchase #7	$73.90	13.440%	$83.8322	$83.83	$83.85	$83.80
7 purchase totals =	$630.31		$666.9340	$666.94	$666.95	$666.90