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	$39.32	8.340%	$42.5993	$42.60	$42.60	$42.60
Purchase #2	$104.25	4.595%	$109.0403	$109.04	$109.05	$109.00
Purchase #3	$52.27	9.201%	$57.0794	$57.08	$57.10	$57.10
Purchase #4	$244.99	7.139%	$262.4798	$262.48	$262.50	$262.50
Purchase #5	$52.52	4.411%	$54.8367	$54.84	$54.85	$54.80
Purchase #6	$67.59	3.472%	$69.9367	$69.94	$69.95	$69.90
Purchase #7	$128.85	10.207%	$142.0017	$142.00	$142.00	$142.00
7 purchase totals =	$689.79		$737.9739	$737.98	$738.05	$737.90