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	$55.81	8.397%	$60.4964	$60.50	$60.50	$60.50
Purchase #2	$128.98	6.376%	$137.2038	$137.20	$137.20	$137.20
Purchase #3	$231.28	11.497%	$257.8703	$257.87	$257.85	$257.90
Purchase #4	$79.81	6.603%	$85.0799	$85.08	$85.10	$85.10
Purchase #5	$76.60	13.461%	$86.9111	$86.91	$86.90	$86.90
Purchase #6	$95.86	5.118%	$100.7661	$100.77	$100.75	$100.80
Purchase #7	$232.90	9.729%	$255.5588	$255.56	$255.55	$255.60
7 purchase totals =	$901.24		$983.8864	$983.89	$983.85	$984.00