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	$60.52	9.810%	$66.457	$66.46	$66.45	$66.50
Purchase #2	$117.82	4.423%	$123.0312	$123.03	$123.05	$123.00
Purchase #3	$82.25	3.123%	$84.8187	$84.82	$84.80	$84.80
Purchase #4	$86.94	13.519%	$98.6934	$98.69	$98.70	$98.70
Purchase #5	$15.50	13.494%	$17.5916	$17.59	$17.60	$17.60
Purchase #6	$34.33	4.126%	$35.7465	$35.75	$35.75	$35.70
Purchase #7	$134.92	12.695%	$152.0481	$152.05	$152.05	$152.00
7 purchase totals =	$532.28		$578.3865	$578.39	$578.40	$578.30