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	$9.30	8.638%	$10.1033	$10.10	$10.10	$10.10
Purchase #2	$81.55	9.433%	$89.2426	$89.24	$89.25	$89.20
Purchase #3	$219.98	6.703%	$234.7253	$234.73	$234.75	$234.70
Purchase #4	$80.53	12.422%	$90.5334	$90.53	$90.55	$90.50
Purchase #5	$145.56	7.468%	$156.4304	$156.43	$156.45	$156.40
Purchase #6	$128.56	12.742%	$144.9411	$144.94	$144.95	$144.90
Purchase #7	$119.87	3.454%	$124.0103	$124.01	$124.00	$124.00
7 purchase totals =	$785.35		$849.9864	$849.98	$850.05	$849.80