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	$139.82	13.308%	$158.4272	$158.43	$158.45	$158.40
Purchase #2	$74.26	11.451%	$82.7635	$82.76	$82.75	$82.80
Purchase #3	$187.89	9.628%	$205.98	$205.98	$206.00	$206.00
Purchase #4	$66.38	5.701%	$70.1643	$70.16	$70.15	$70.20
Purchase #5	$46.27	6.714%	$49.3766	$49.38	$49.40	$49.40
Purchase #6	$75.93	12.766%	$85.6232	$85.62	$85.60	$85.60
Purchase #7	$241.62	12.367%	$271.5011	$271.50	$271.50	$271.50
7 purchase totals =	$832.17		$923.8359	$923.83	$923.85	$923.90