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	$70.88	5.619%	$74.8627	$74.86	$74.85	$74.90
Purchase #2	$97.89	11.864%	$109.5037	$109.50	$109.50	$109.50
Purchase #3	$164.82	13.128%	$186.4576	$186.46	$186.45	$186.50
Purchase #4	$97.89	10.389%	$108.0598	$108.06	$108.05	$108.10
Purchase #5	$105.46	5.311%	$111.061	$111.06	$111.05	$111.10
Purchase #6	$204.88	8.816%	$222.9422	$222.94	$222.95	$222.90
Purchase #7	$121.66	12.287%	$136.6084	$136.61	$136.60	$136.60
7 purchase totals =	$863.48		$949.4954	$949.49	$949.45	$949.60