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	$58.90	5.758%	$62.2915	$62.29	$62.30	$62.30
Purchase #2	$173.37	11.655%	$193.5763	$193.58	$193.60	$193.60
Purchase #3	$90.94	8.115%	$98.3198	$98.32	$98.30	$98.30
Purchase #4	$88.78	7.571%	$95.5015	$95.50	$95.50	$95.50
Purchase #5	$63.42	13.615%	$72.0546	$72.05	$72.05	$72.10
Purchase #6	$217.66	8.644%	$236.4745	$236.47	$236.45	$236.50
Purchase #7	$139.52	4.160%	$145.324	$145.32	$145.30	$145.30
7 purchase totals =	$832.59		$903.5422	$903.53	$903.50	$903.60