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	$9.27	4.664%	$9.7024	$9.70	$9.70	$9.70
Purchase #2	$183.28	12.218%	$205.6732	$205.67	$205.65	$205.70
Purchase #3	$141.96	11.659%	$158.5111	$158.51	$158.50	$158.50
Purchase #4	$81.72	10.792%	$90.5392	$90.54	$90.55	$90.50
Purchase #5	$81.67	11.306%	$90.9036	$90.90	$90.90	$90.90
Purchase #6	$221.69	4.377%	$231.3934	$231.39	$231.40	$231.40
Purchase #7	$161.89	13.347%	$183.4975	$183.50	$183.50	$183.50
7 purchase totals =	$881.48		$970.2204	$970.21	$970.20	$970.20