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	$93.29	7.379%	$100.1739	$100.17	$100.15	$100.20
Purchase #2	$204.46	10.856%	$226.6562	$226.66	$226.65	$226.70
Purchase #3	$131.82	6.868%	$140.8734	$140.87	$140.85	$140.90
Purchase #4	$209.28	7.641%	$225.2711	$225.27	$225.25	$225.30
Purchase #5	$66.42	4.135%	$69.1665	$69.17	$69.15	$69.20
Purchase #6	$225.44	13.325%	$255.4799	$255.48	$255.50	$255.50
Purchase #7	$9.69	10.344%	$10.6923	$10.69	$10.70	$10.70
7 purchase totals =	$940.40		$1,028.3133	$1,028.31	$1,028.25	$1,028.50