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	$134.25	6.836%	$143.4273	$143.43	$143.45	$143.40
Purchase #2	$29.72	9.447%	$32.5276	$32.53	$32.55	$32.50
Purchase #3	$137.91	3.138%	$142.2376	$142.24	$142.25	$142.20
Purchase #4	$29.39	11.218%	$32.687	$32.69	$32.70	$32.70
Purchase #5	$60.58	4.640%	$63.3909	$63.39	$63.40	$63.40
Purchase #6	$112.42	7.746%	$121.1281	$121.13	$121.15	$121.10
Purchase #7	$200.41	12.507%	$225.4753	$225.48	$225.50	$225.50
7 purchase totals =	$704.68		$760.8738	$760.89	$761.00	$760.80