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	$108.75	13.503%	$123.4345	$123.43	$123.45	$123.40
Purchase #2	$29.26	12.314%	$32.8631	$32.86	$32.85	$32.90
Purchase #3	$70.77	7.192%	$75.8598	$75.86	$75.85	$75.90
Purchase #4	$23.81	4.541%	$24.8912	$24.89	$24.90	$24.90
Purchase #5	$37.45	5.178%	$39.3892	$39.39	$39.40	$39.40
Purchase #6	$208.71	6.756%	$222.8104	$222.81	$222.80	$222.80
Purchase #7	$95.87	13.265%	$108.5872	$108.59	$108.60	$108.60
7 purchase totals =	$574.62		$627.8354	$627.83	$627.85	$627.90