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	$145.93	13.488%	$165.613	$165.61	$165.60	$165.60
Purchase #2	$202.35	6.612%	$215.7294	$215.73	$215.75	$215.70
Purchase #3	$63.49	9.241%	$69.3571	$69.36	$69.35	$69.40
Purchase #4	$26.27	5.391%	$27.6862	$27.69	$27.70	$27.70
Purchase #5	$78.63	8.733%	$85.4968	$85.50	$85.50	$85.50
Purchase #6	$59.25	11.123%	$65.8404	$65.84	$65.85	$65.80
Purchase #7	$103.49	5.184%	$108.8549	$108.85	$108.85	$108.90
7 purchase totals =	$679.41		$738.5778	$738.58	$738.60	$738.60