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	$85.45	10.108%	$94.0873	$94.09	$94.10	$94.10
Purchase #2	$135.87	9.570%	$148.8728	$148.87	$148.85	$148.90
Purchase #3	$18.88	11.508%	$21.0527	$21.05	$21.05	$21.10
Purchase #4	$128.43	11.714%	$143.4743	$143.47	$143.45	$143.50
Purchase #5	$183.49	12.772%	$206.9253	$206.93	$206.95	$206.90
Purchase #6	$40.88	11.313%	$45.5048	$45.50	$45.50	$45.50
Purchase #7	$237.56	7.370%	$255.0682	$255.07	$255.05	$255.10
7 purchase totals =	$830.56		$914.9854	$914.98	$914.95	$915.10