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	$90.89	6.153%	$96.4825	$96.48	$96.50	$96.50
Purchase #2	$81.39	8.139%	$88.0143	$88.01	$88.00	$88.00
Purchase #3	$182.90	12.587%	$205.9216	$205.92	$205.90	$205.90
Purchase #4	$98.69	10.719%	$109.2686	$109.27	$109.25	$109.30
Purchase #5	$99.90	12.558%	$112.4454	$112.45	$112.45	$112.40
Purchase #6	$166.70	6.679%	$177.8339	$177.83	$177.85	$177.80
Purchase #7	$157.61	8.259%	$170.627	$170.63	$170.65	$170.60
7 purchase totals =	$878.08		$960.5933	$960.59	$960.60	$960.50