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	$79.59	13.703%	$90.4962	$90.50	$90.50	$90.50
Purchase #2	$106.34	13.389%	$120.5779	$120.58	$120.60	$120.60
Purchase #3	$62.96	4.127%	$65.5584	$65.56	$65.55	$65.60
Purchase #4	$159.73	8.598%	$173.4636	$173.46	$173.45	$173.50
Purchase #5	$76.91	11.317%	$85.6139	$85.61	$85.60	$85.60
Purchase #6	$82.32	12.621%	$92.7096	$92.71	$92.70	$92.70
Purchase #7	$114.59	12.198%	$128.5677	$128.57	$128.55	$128.60
7 purchase totals =	$682.44		$756.9873	$756.99	$756.95	$757.10