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	$131.31	9.430%	$143.6925	$143.69	$143.70	$143.70
Purchase #2	$84.31	6.166%	$89.5086	$89.51	$89.50	$89.50
Purchase #3	$57.81	5.686%	$61.0971	$61.10	$61.10	$61.10
Purchase #4	$115.68	8.189%	$125.153	$125.15	$125.15	$125.20
Purchase #5	$241.32	5.572%	$254.7664	$254.77	$254.75	$254.80
Purchase #6	$24.74	12.667%	$27.8738	$27.87	$27.85	$27.90
Purchase #7	$128.25	13.712%	$145.8356	$145.84	$145.85	$145.80
7 purchase totals =	$783.42		$847.9270	$847.93	$847.90	$848.00