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	$194.35	13.542%	$220.6689	$220.67	$220.65	$220.70
Purchase #2	$55.44	7.395%	$59.5398	$59.54	$59.55	$59.50
Purchase #3	$91.74	9.678%	$100.6186	$100.62	$100.60	$100.60
Purchase #4	$50.78	4.228%	$52.927	$52.93	$52.95	$52.90
Purchase #5	$165.91	12.365%	$186.4248	$186.42	$186.40	$186.40
Purchase #6	$200.35	7.271%	$214.9174	$214.92	$214.90	$214.90
Purchase #7	$23.73	7.108%	$25.4167	$25.42	$25.40	$25.40
7 purchase totals =	$782.30		$860.5132	$860.52	$860.45	$860.40