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	$47.75	8.285%	$51.7061	$51.71	$51.70	$51.70
Purchase #2	$63.83	5.773%	$67.5149	$67.51	$67.50	$67.50
Purchase #3	$200.87	10.705%	$222.3731	$222.37	$222.35	$222.40
Purchase #4	$46.83	8.613%	$50.8635	$50.86	$50.85	$50.90
Purchase #5	$13.40	6.644%	$14.2903	$14.29	$14.30	$14.30
Purchase #6	$196.39	10.446%	$216.9049	$216.90	$216.90	$216.90
Purchase #7	$206.64	10.341%	$228.0086	$228.01	$228.00	$228.00
7 purchase totals =	$775.71		$851.6614	$851.65	$851.60	$851.70