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	$66.52	8.803%	$72.3758	$72.38	$72.40	$72.40
Purchase #2	$118.69	8.201%	$128.4238	$128.42	$128.40	$128.40
Purchase #3	$61.85	12.454%	$69.5528	$69.55	$69.55	$69.60
Purchase #4	$34.60	12.449%	$38.9074	$38.91	$38.90	$38.90
Purchase #5	$24.43	11.867%	$27.3291	$27.33	$27.35	$27.30
Purchase #6	$136.78	5.302%	$144.0321	$144.03	$144.05	$144.00
Purchase #7	$72.95	8.423%	$79.0946	$79.09	$79.10	$79.10
7 purchase totals =	$515.82		$559.7156	$559.71	$559.75	$559.70