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	$216.85	6.654%	$231.2792	$231.28	$231.30	$231.30
Purchase #2	$140.45	8.242%	$152.0259	$152.03	$152.05	$152.00
Purchase #3	$46.62	13.603%	$52.9617	$52.96	$52.95	$53.00
Purchase #4	$43.36	6.239%	$46.0652	$46.07	$46.05	$46.10
Purchase #5	$91.32	10.287%	$100.7141	$100.71	$100.70	$100.70
Purchase #6	$12.61	11.730%	$14.0892	$14.09	$14.10	$14.10
Purchase #7	$47.48	8.859%	$51.6863	$51.69	$51.70	$51.70
7 purchase totals =	$598.69		$648.8216	$648.83	$648.85	$648.90