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	$20.66	5.854%	$21.8694	$21.87	$21.85	$21.90
Purchase #2	$128.37	8.546%	$139.3405	$139.34	$139.35	$139.30
Purchase #3	$126.66	13.564%	$143.8402	$143.84	$143.85	$143.80
Purchase #4	$43.91	10.222%	$48.3985	$48.40	$48.40	$48.40
Purchase #5	$193.85	3.175%	$200.0047	$200.00	$200.00	$200.00
Purchase #6	$85.95	7.759%	$92.6189	$92.62	$92.60	$92.60
Purchase #7	$156.49	12.144%	$175.4941	$175.49	$175.50	$175.50
7 purchase totals =	$755.89		$821.5663	$821.56	$821.55	$821.50