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	$172.43	5.757%	$182.3568	$182.36	$182.35	$182.40
Purchase #2	$45.89	8.211%	$49.658	$49.66	$49.65	$49.70
Purchase #3	$118.93	8.253%	$128.7453	$128.75	$128.75	$128.70
Purchase #4	$110.66	9.668%	$121.3586	$121.36	$121.35	$121.40
Purchase #5	$40.31	12.618%	$45.3963	$45.40	$45.40	$45.40
Purchase #6	$18.79	6.496%	$20.0106	$20.01	$20.00	$20.00
Purchase #7	$103.37	7.644%	$111.2716	$111.27	$111.25	$111.30
7 purchase totals =	$610.38		$658.7972	$658.81	$658.75	$658.90