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	$142.38	13.627%	$161.7821	$161.78	$161.80	$161.80
Purchase #2	$129.36	11.202%	$143.8509	$143.85	$143.85	$143.90
Purchase #3	$197.45	7.768%	$212.7879	$212.79	$212.80	$212.80
Purchase #4	$107.45	4.181%	$111.9425	$111.94	$111.95	$111.90
Purchase #5	$113.57	12.799%	$128.1058	$128.11	$128.10	$128.10
Purchase #6	$48.49	7.166%	$51.9648	$51.96	$51.95	$52.00
Purchase #7	$52.33	4.340%	$54.6011	$54.60	$54.60	$54.60
7 purchase totals =	$791.03		$865.0351	$865.03	$865.05	$865.10