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	$112.46	4.281%	$117.2744	$117.27	$117.25	$117.30
Purchase #2	$200.92	13.147%	$227.335	$227.34	$227.35	$227.30
Purchase #3	$74.32	8.508%	$80.6431	$80.64	$80.65	$80.60
Purchase #4	$38.59	10.863%	$42.782	$42.78	$42.80	$42.80
Purchase #5	$19.30	5.676%	$20.3955	$20.40	$20.40	$20.40
Purchase #6	$20.88	3.380%	$21.5857	$21.59	$21.60	$21.60
Purchase #7	$158.79	6.496%	$169.105	$169.11	$169.10	$169.10
7 purchase totals =	$625.26		$679.1207	$679.13	$679.15	$679.10