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	$225.97	6.874%	$241.5032	$241.50	$241.50	$241.50
Purchase #2	$74.47	5.413%	$78.5011	$78.50	$78.50	$78.50
Purchase #3	$84.93	6.559%	$90.5006	$90.50	$90.50	$90.50
Purchase #4	$59.92	12.299%	$67.2896	$67.29	$67.30	$67.30
Purchase #5	$131.51	9.114%	$143.4958	$143.50	$143.50	$143.50
Purchase #6	$145.93	8.637%	$158.534	$158.53	$158.55	$158.50
Purchase #7	$126.82	13.728%	$144.2298	$144.23	$144.25	$144.20
7 purchase totals =	$849.55		$924.0541	$924.05	$924.10	$924.00