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	$19.29	11.316%	$21.4729	$21.47	$21.45	$21.50
Purchase #2	$217.82	4.115%	$226.7833	$226.78	$226.80	$226.80
Purchase #3	$238.42	13.191%	$269.87	$269.87	$269.85	$269.90
Purchase #4	$18.88	9.410%	$20.6566	$20.66	$20.65	$20.70
Purchase #5	$247.57	3.673%	$256.6632	$256.66	$256.65	$256.70
Purchase #6	$114.80	11.354%	$127.8344	$127.83	$127.85	$127.80
Purchase #7	$133.72	3.611%	$138.5486	$138.55	$138.55	$138.50
7 purchase totals =	$990.50		$1,061.8290	$1,061.82	$1,061.80	$1,061.90