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	$62.39	3.756%	$64.7334	$64.73	$64.75	$64.70
Purchase #2	$83.72	10.692%	$92.6713	$92.67	$92.65	$92.70
Purchase #3	$85.62	11.682%	$95.6221	$95.62	$95.60	$95.60
Purchase #4	$12.54	9.412%	$13.7203	$13.72	$13.70	$13.70
Purchase #5	$80.70	3.231%	$83.3074	$83.31	$83.30	$83.30
Purchase #6	$34.89	12.695%	$39.3193	$39.32	$39.30	$39.30
Purchase #7	$130.89	6.748%	$139.7225	$139.72	$139.70	$139.70
7 purchase totals =	$490.75		$529.0963	$529.09	$529.00	$529.00