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	$119.32	3.583%	$123.5952	$123.60	$123.60	$123.60
Purchase #2	$61.39	8.142%	$66.3884	$66.39	$66.40	$66.40
Purchase #3	$177.72	13.800%	$202.2454	$202.25	$202.25	$202.20
Purchase #4	$139.78	12.362%	$157.0596	$157.06	$157.05	$157.10
Purchase #5	$123.89	12.812%	$139.7628	$139.76	$139.75	$139.80
Purchase #6	$137.90	5.579%	$145.5934	$145.59	$145.60	$145.60
Purchase #7	$13.70	11.670%	$15.2988	$15.30	$15.30	$15.30
7 purchase totals =	$773.70		$849.9436	$849.95	$849.95	$850.00