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	$67.50	6.147%	$71.6492	$71.65	$71.65	$71.60
Purchase #2	$141.84	10.638%	$156.9289	$156.93	$156.95	$156.90
Purchase #3	$59.98	6.514%	$63.8871	$63.89	$63.90	$63.90
Purchase #4	$59.67	4.698%	$62.4733	$62.47	$62.45	$62.50
Purchase #5	$60.87	7.689%	$65.5503	$65.55	$65.55	$65.60
Purchase #6	$37.62	8.515%	$40.8233	$40.82	$40.80	$40.80
Purchase #7	$8.47	8.458%	$9.1864	$9.19	$9.20	$9.20
7 purchase totals =	$435.95		$470.4985	$470.50	$470.50	$470.50