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	$161.38	5.368%	$170.0429	$170.04	$170.05	$170.00
Purchase #2	$94.50	9.336%	$103.3225	$103.32	$103.30	$103.30
Purchase #3	$60.84	10.733%	$67.37	$67.37	$67.35	$67.40
Purchase #4	$248.75	5.357%	$262.0755	$262.08	$262.10	$262.10
Purchase #5	$228.69	11.767%	$255.6	$255.60	$255.60	$255.60
Purchase #6	$60.33	11.468%	$67.2486	$67.25	$67.25	$67.20
Purchase #7	$59.37	13.397%	$67.3238	$67.32	$67.30	$67.30
7 purchase totals =	$913.86		$992.9833	$992.98	$992.95	$992.90