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	$40.68	13.574%	$46.2019	$46.20	$46.20	$46.20
Purchase #2	$200.59	11.846%	$224.3519	$224.35	$224.35	$224.40
Purchase #3	$72.98	13.408%	$82.7652	$82.77	$82.75	$82.80
Purchase #4	$104.58	7.456%	$112.3775	$112.38	$112.40	$112.40
Purchase #5	$66.99	8.310%	$72.5569	$72.56	$72.55	$72.60
Purchase #6	$219.70	6.387%	$233.7322	$233.73	$233.75	$233.70
Purchase #7	$179.39	4.724%	$187.8644	$187.86	$187.85	$187.90
7 purchase totals =	$884.91		$959.8500	$959.85	$959.85	$960.00