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	$52.81	8.830%	$57.4731	$57.47	$57.45	$57.50
Purchase #2	$108.78	9.241%	$118.8324	$118.83	$118.85	$118.80
Purchase #3	$179.32	4.208%	$186.8658	$186.87	$186.85	$186.90
Purchase #4	$235.75	11.328%	$262.4558	$262.46	$262.45	$262.50
Purchase #5	$52.71	5.122%	$55.4098	$55.41	$55.40	$55.40
Purchase #6	$198.27	10.338%	$218.7672	$218.77	$218.75	$218.80
Purchase #7	$112.84	8.568%	$122.5081	$122.51	$122.50	$122.50
7 purchase totals =	$940.48		$1,022.3122	$1,022.32	$1,022.25	$1,022.40