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	$78.53	5.614%	$82.9387	$82.94	$82.95	$82.90
Purchase #2	$31.43	9.200%	$34.3216	$34.32	$34.30	$34.30
Purchase #3	$125.73	9.552%	$137.7397	$137.74	$137.75	$137.70
Purchase #4	$242.48	6.390%	$257.9745	$257.97	$257.95	$258.00
Purchase #5	$114.96	11.635%	$128.3356	$128.34	$128.35	$128.30
Purchase #6	$95.42	10.232%	$105.1834	$105.18	$105.20	$105.20
Purchase #7	$240.52	12.169%	$269.7889	$269.79	$269.80	$269.80
7 purchase totals =	$929.07		$1,016.2824	$1,016.28	$1,016.30	$1,016.20