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	$139.33	11.427%	$155.2512	$155.25	$155.25	$155.30
Purchase #2	$110.95	11.544%	$123.7581	$123.76	$123.75	$123.80
Purchase #3	$66.57	13.296%	$75.4211	$75.42	$75.40	$75.40
Purchase #4	$17.38	8.141%	$18.7949	$18.79	$18.80	$18.80
Purchase #5	$191.43	4.744%	$200.5114	$200.51	$200.50	$200.50
Purchase #6	$140.67	11.314%	$156.5854	$156.59	$156.60	$156.60
Purchase #7	$76.60	9.573%	$83.9329	$83.93	$83.95	$83.90
7 purchase totals =	$742.93		$814.2550	$814.25	$814.25	$814.30