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	$46.51	9.702%	$51.0224	$51.02	$51.00	$51.00
Purchase #2	$206.88	13.508%	$234.8254	$234.83	$234.85	$234.80
Purchase #3	$130.62	9.637%	$143.2078	$143.21	$143.20	$143.20
Purchase #4	$5.89	9.733%	$6.4633	$6.46	$6.45	$6.50
Purchase #5	$107.89	13.851%	$122.8338	$122.83	$122.85	$122.80
Purchase #6	$173.88	6.554%	$185.2761	$185.28	$185.30	$185.30
Purchase #7	$83.93	6.753%	$89.5978	$89.60	$89.60	$89.60
7 purchase totals =	$755.60		$833.2266	$833.23	$833.25	$833.20