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	$48.96	3.314%	$50.5825	$50.58	$50.60	$50.60
Purchase #2	$90.76	13.652%	$103.1506	$103.15	$103.15	$103.20
Purchase #3	$124.47	12.400%	$139.9043	$139.90	$139.90	$139.90
Purchase #4	$182.96	4.697%	$191.5536	$191.55	$191.55	$191.60
Purchase #5	$150.72	3.287%	$155.6742	$155.67	$155.65	$155.70
Purchase #6	$44.32	9.672%	$48.6066	$48.61	$48.60	$48.60
Purchase #7	$34.70	13.395%	$39.3481	$39.35	$39.35	$39.30
7 purchase totals =	$676.89		$728.8199	$728.81	$728.80	$728.90