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	$60.82	10.408%	$67.1501	$67.15	$67.15	$67.20
Purchase #2	$133.50	10.674%	$147.7498	$147.75	$147.75	$147.70
Purchase #3	$178.67	11.676%	$199.5315	$199.53	$199.55	$199.50
Purchase #4	$144.76	9.741%	$158.8611	$158.86	$158.85	$158.90
Purchase #5	$139.82	10.584%	$154.6185	$154.62	$154.60	$154.60
Purchase #6	$32.32	6.691%	$34.4825	$34.48	$34.50	$34.50
Purchase #7	$62.67	5.569%	$66.1601	$66.16	$66.15	$66.20
7 purchase totals =	$752.56		$828.5536	$828.55	$828.55	$828.60