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	$218.87	9.378%	$239.3956	$239.40	$239.40	$239.40
Purchase #2	$134.31	7.744%	$144.711	$144.71	$144.70	$144.70
Purchase #3	$72.97	13.785%	$83.0289	$83.03	$83.05	$83.00
Purchase #4	$98.67	10.694%	$109.2218	$109.22	$109.20	$109.20
Purchase #5	$177.54	3.329%	$183.4503	$183.45	$183.45	$183.50
Purchase #6	$123.55	6.400%	$131.4572	$131.46	$131.45	$131.50
Purchase #7	$107.77	4.711%	$112.847	$112.85	$112.85	$112.80
7 purchase totals =	$933.68		$1,004.1118	$1,004.12	$1,004.10	$1,004.10