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	$96.49	9.588%	$105.7415	$105.74	$105.75	$105.70
Purchase #2	$73.57	10.528%	$81.3154	$81.32	$81.30	$81.30
Purchase #3	$133.38	4.150%	$138.9153	$138.92	$138.90	$138.90
Purchase #4	$103.32	8.335%	$111.9317	$111.93	$111.95	$111.90
Purchase #5	$103.92	5.524%	$109.6605	$109.66	$109.65	$109.70
Purchase #6	$21.82	7.175%	$23.3856	$23.39	$23.40	$23.40
Purchase #7	$53.89	7.434%	$57.8962	$57.90	$57.90	$57.90
7 purchase totals =	$586.39		$628.8462	$628.86	$628.85	$628.80