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	$245.50	7.829%	$264.7202	$264.72	$264.70	$264.70
Purchase #2	$136.76	6.641%	$145.8422	$145.84	$145.85	$145.80
Purchase #3	$200.27	10.853%	$222.0053	$222.01	$222.00	$222.00
Purchase #4	$81.42	10.197%	$89.7224	$89.72	$89.70	$89.70
Purchase #5	$119.87	4.637%	$125.4284	$125.43	$125.45	$125.40
Purchase #6	$81.66	8.410%	$88.5276	$88.53	$88.55	$88.50
Purchase #7	$126.68	5.658%	$133.8476	$133.85	$133.85	$133.80
7 purchase totals =	$992.16		$1,070.0937	$1,070.10	$1,070.10	$1,069.90