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	$92.68	8.367%	$100.4345	$100.43	$100.45	$100.40
Purchase #2	$67.49	4.397%	$70.4575	$70.46	$70.45	$70.50
Purchase #3	$144.78	3.795%	$150.2744	$150.27	$150.25	$150.30
Purchase #4	$239.72	9.299%	$262.0116	$262.01	$262.00	$262.00
Purchase #5	$161.48	11.770%	$180.4862	$180.49	$180.50	$180.50
Purchase #6	$33.58	6.667%	$35.8188	$35.82	$35.80	$35.80
Purchase #7	$97.89	5.800%	$103.5676	$103.57	$103.55	$103.60
7 purchase totals =	$837.62		$903.0506	$903.05	$903.00	$903.10