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	$170.77	6.856%	$182.478	$182.48	$182.50	$182.50
Purchase #2	$173.28	13.569%	$196.7924	$196.79	$196.80	$196.80
Purchase #3	$48.89	9.342%	$53.4573	$53.46	$53.45	$53.50
Purchase #4	$179.99	9.398%	$196.9055	$196.91	$196.90	$196.90
Purchase #5	$20.36	11.176%	$22.6354	$22.64	$22.65	$22.60
Purchase #6	$178.78	6.851%	$191.0282	$191.03	$191.05	$191.00
Purchase #7	$34.33	3.652%	$35.5837	$35.58	$35.60	$35.60
7 purchase totals =	$806.40		$878.8805	$878.89	$878.95	$878.90