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	$101.29	7.455%	$108.8412	$108.84	$108.85	$108.80
Purchase #2	$82.77	8.160%	$89.524	$89.52	$89.50	$89.50
Purchase #3	$95.32	5.445%	$100.5102	$100.51	$100.50	$100.50
Purchase #4	$148.93	9.386%	$162.9086	$162.91	$162.90	$162.90
Purchase #5	$131.94	9.612%	$144.6221	$144.62	$144.60	$144.60
Purchase #6	$50.73	10.553%	$56.0835	$56.08	$56.10	$56.10
Purchase #7	$219.93	8.733%	$239.1365	$239.14	$239.15	$239.10
7 purchase totals =	$830.91		$901.6261	$901.62	$901.60	$901.50