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	$240.78	11.280%	$267.94	$267.94	$267.95	$267.90
Purchase #2	$72.97	6.772%	$77.9115	$77.91	$77.90	$77.90
Purchase #3	$244.57	12.246%	$274.52	$274.52	$274.50	$274.50
Purchase #4	$73.93	3.495%	$76.5139	$76.51	$76.50	$76.50
Purchase #5	$19.48	4.487%	$20.3541	$20.35	$20.35	$20.40
Purchase #6	$35.25	6.128%	$37.4101	$37.41	$37.40	$37.40
Purchase #7	$48.49	7.790%	$52.2674	$52.27	$52.25	$52.30
7 purchase totals =	$735.47		$806.9170	$806.91	$806.85	$806.90