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	$133.50	6.389%	$142.0293	$142.03	$142.05	$142.00
Purchase #2	$30.89	12.731%	$34.8226	$34.82	$34.80	$34.80
Purchase #3	$61.54	4.137%	$64.0859	$64.09	$64.10	$64.10
Purchase #4	$126.72	3.590%	$131.2692	$131.27	$131.25	$131.30
Purchase #5	$26.39	12.838%	$29.7779	$29.78	$29.80	$29.80
Purchase #6	$83.64	10.478%	$92.4038	$92.40	$92.40	$92.40
Purchase #7	$87.43	9.611%	$95.8329	$95.83	$95.85	$95.80
7 purchase totals =	$550.11		$590.2216	$590.22	$590.25	$590.20