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	$189.95	13.352%	$215.3121	$215.31	$215.30	$215.30
Purchase #2	$49.70	3.418%	$51.3987	$51.40	$51.40	$51.40
Purchase #3	$113.30	8.131%	$122.5124	$122.51	$122.50	$122.50
Purchase #4	$21.38	5.722%	$22.6034	$22.60	$22.60	$22.60
Purchase #5	$13.69	13.846%	$15.5855	$15.59	$15.60	$15.60
Purchase #6	$76.78	3.292%	$79.3076	$79.31	$79.30	$79.30
Purchase #7	$152.51	4.168%	$158.8666	$158.87	$158.85	$158.90
7 purchase totals =	$617.31		$665.5863	$665.59	$665.55	$665.60