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	$172.66	9.579%	$189.1991	$189.20	$189.20	$189.20
Purchase #2	$228.38	9.795%	$250.7498	$250.75	$250.75	$250.70
Purchase #3	$136.92	5.576%	$144.5547	$144.55	$144.55	$144.60
Purchase #4	$172.46	6.502%	$183.6733	$183.67	$183.65	$183.70
Purchase #5	$126.29	13.658%	$143.5387	$143.54	$143.55	$143.50
Purchase #6	$112.80	12.708%	$127.1346	$127.13	$127.15	$127.10
Purchase #7	$25.80	12.602%	$29.0513	$29.05	$29.05	$29.10
7 purchase totals =	$975.31		$1,067.9015	$1,067.89	$1,067.90	$1,067.90