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	$37.96	6.384%	$40.3834	$40.38	$40.40	$40.40
Purchase #2	$247.50	3.321%	$255.7195	$255.72	$255.70	$255.70
Purchase #3	$93.42	7.362%	$100.2976	$100.30	$100.30	$100.30
Purchase #4	$187.99	5.860%	$199.0062	$199.01	$199.00	$199.00
Purchase #5	$5.52	4.758%	$5.7826	$5.78	$5.80	$5.80
Purchase #6	$127.87	12.235%	$143.5149	$143.51	$143.50	$143.50
Purchase #7	$179.66	11.535%	$200.3838	$200.38	$200.40	$200.40
7 purchase totals =	$879.92		$945.0880	$945.08	$945.10	$945.10