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	$200.82	6.395%	$213.6624	$213.66	$213.65	$213.70
Purchase #2	$111.83	13.746%	$127.2022	$127.20	$127.20	$127.20
Purchase #3	$138.95	8.380%	$150.594	$150.59	$150.60	$150.60
Purchase #4	$20.88	3.138%	$21.5352	$21.54	$21.55	$21.50
Purchase #5	$51.36	3.718%	$53.2696	$53.27	$53.25	$53.30
Purchase #6	$132.72	13.765%	$150.9889	$150.99	$151.00	$151.00
Purchase #7	$119.67	6.581%	$127.5455	$127.55	$127.55	$127.50
7 purchase totals =	$776.23		$844.7978	$844.80	$844.80	$844.80