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	$197.88	6.206%	$210.1604	$210.16	$210.15	$210.20
Purchase #2	$208.83	5.377%	$220.0588	$220.06	$220.05	$220.10
Purchase #3	$132.57	13.473%	$150.4312	$150.43	$150.45	$150.40
Purchase #4	$143.95	10.114%	$158.5091	$158.51	$158.50	$158.50
Purchase #5	$19.83	3.519%	$20.5278	$20.53	$20.55	$20.50
Purchase #6	$86.83	13.736%	$98.757	$98.76	$98.75	$98.80
Purchase #7	$115.52	5.142%	$121.46	$121.46	$121.45	$121.50
7 purchase totals =	$905.41		$979.9043	$979.91	$979.90	$980.00