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	$83.40	5.497%	$87.9845	$87.98	$88.00	$88.00
Purchase #2	$107.56	8.506%	$116.7091	$116.71	$116.70	$116.70
Purchase #3	$166.56	13.705%	$189.387	$189.39	$189.40	$189.40
Purchase #4	$75.50	5.153%	$79.3905	$79.39	$79.40	$79.40
Purchase #5	$224.28	11.667%	$250.4467	$250.45	$250.45	$250.40
Purchase #6	$100.76	4.771%	$105.5673	$105.57	$105.55	$105.60
Purchase #7	$114.84	11.793%	$128.3831	$128.38	$128.40	$128.40
7 purchase totals =	$872.90		$957.8682	$957.87	$957.90	$957.90