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	$192.62	6.174%	$204.5124	$204.51	$204.50	$204.50
Purchase #2	$178.50	11.840%	$199.6344	$199.63	$199.65	$199.60
Purchase #3	$190.57	4.787%	$199.6926	$199.69	$199.70	$199.70
Purchase #4	$138.60	11.691%	$154.8037	$154.80	$154.80	$154.80
Purchase #5	$120.86	5.763%	$127.8252	$127.83	$127.85	$127.80
Purchase #6	$174.40	8.598%	$189.3949	$189.39	$189.40	$189.40
Purchase #7	$147.37	10.341%	$162.6095	$162.61	$162.60	$162.60
7 purchase totals =	$1,142.92		$1,238.4727	$1,238.46	$1,238.50	$1,238.40