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	$169.95	4.821%	$178.1433	$178.14	$178.15	$178.10
Purchase #2	$54.71	9.366%	$59.8341	$59.83	$59.85	$59.80
Purchase #3	$124.76	12.843%	$140.7829	$140.78	$140.80	$140.80
Purchase #4	$30.44	7.134%	$32.6116	$32.61	$32.60	$32.60
Purchase #5	$13.78	7.762%	$14.8496	$14.85	$14.85	$14.80
Purchase #6	$130.97	5.309%	$137.9232	$137.92	$137.90	$137.90
Purchase #7	$183.76	12.554%	$206.8292	$206.83	$206.85	$206.80
7 purchase totals =	$708.37		$770.9739	$770.96	$771.00	$770.80