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	$204.58	11.345%	$227.7896	$227.79	$227.80	$227.80
Purchase #2	$169.72	11.819%	$189.7792	$189.78	$189.80	$189.80
Purchase #3	$29.67	6.815%	$31.692	$31.69	$31.70	$31.70
Purchase #4	$49.58	3.496%	$51.3133	$51.31	$51.30	$51.30
Purchase #5	$84.45	7.294%	$90.6098	$90.61	$90.60	$90.60
Purchase #6	$247.45	4.375%	$258.2759	$258.28	$258.30	$258.30
Purchase #7	$65.47	7.491%	$70.3744	$70.37	$70.35	$70.40
7 purchase totals =	$850.92		$919.8342	$919.83	$919.85	$919.90