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	$39.30	3.209%	$40.5611	$40.56	$40.55	$40.60
Purchase #2	$103.27	10.749%	$114.3705	$114.37	$114.35	$114.40
Purchase #3	$131.65	5.792%	$139.2752	$139.28	$139.30	$139.30
Purchase #4	$15.45	10.633%	$17.0928	$17.09	$17.10	$17.10
Purchase #5	$210.93	11.845%	$235.9147	$235.91	$235.90	$235.90
Purchase #6	$178.54	10.197%	$196.7457	$196.75	$196.75	$196.70
Purchase #7	$117.46	9.794%	$128.964	$128.96	$128.95	$129.00
7 purchase totals =	$796.60		$872.9240	$872.92	$872.90	$873.00