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	$131.44	9.653%	$144.1279	$144.13	$144.15	$144.10
Purchase #2	$42.72	11.456%	$47.614	$47.61	$47.60	$47.60
Purchase #3	$87.78	12.241%	$98.5251	$98.53	$98.55	$98.50
Purchase #4	$179.85	3.394%	$185.9541	$185.95	$185.95	$186.00
Purchase #5	$235.47	8.658%	$255.857	$255.86	$255.85	$255.90
Purchase #6	$34.96	8.141%	$37.8061	$37.81	$37.80	$37.80
Purchase #7	$65.34	11.845%	$73.0795	$73.08	$73.10	$73.10
7 purchase totals =	$777.56		$842.9637	$842.97	$843.00	$843.00