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	$78.81	12.794%	$88.893	$88.89	$88.90	$88.90
Purchase #2	$190.77	13.509%	$216.5411	$216.54	$216.55	$216.50
Purchase #3	$87.56	3.659%	$90.7638	$90.76	$90.75	$90.80
Purchase #4	$71.58	3.780%	$74.2857	$74.29	$74.30	$74.30
Purchase #5	$177.65	6.485%	$189.1706	$189.17	$189.15	$189.20
Purchase #6	$175.51	10.779%	$194.4282	$194.43	$194.45	$194.40
Purchase #7	$25.60	8.554%	$27.7898	$27.79	$27.80	$27.80
7 purchase totals =	$807.48		$881.8722	$881.87	$881.90	$881.90