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	$40.93	6.721%	$43.6809	$43.68	$43.70	$43.70
Purchase #2	$56.85	4.826%	$59.5936	$59.59	$59.60	$59.60
Purchase #3	$243.61	9.643%	$267.1013	$267.10	$267.10	$267.10
Purchase #4	$100.75	10.872%	$111.7035	$111.70	$111.70	$111.70
Purchase #5	$22.95	4.458%	$23.9731	$23.97	$23.95	$24.00
Purchase #6	$7.29	11.147%	$8.1026	$8.10	$8.10	$8.10
Purchase #7	$32.72	6.243%	$34.7627	$34.76	$34.75	$34.80
7 purchase totals =	$505.10		$548.9177	$548.90	$548.90	$549.00