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	$9.75	13.722%	$11.0879	$11.09	$11.10	$11.10
Purchase #2	$22.32	11.785%	$24.9504	$24.95	$24.95	$25.00
Purchase #3	$167.93	13.667%	$190.881	$190.88	$190.90	$190.90
Purchase #4	$98.31	7.376%	$105.5613	$105.56	$105.55	$105.60
Purchase #5	$182.42	4.333%	$190.3243	$190.32	$190.30	$190.30
Purchase #6	$18.85	10.500%	$20.8293	$20.83	$20.85	$20.80
Purchase #7	$15.43	13.169%	$17.462	$17.46	$17.45	$17.50
7 purchase totals =	$515.01		$561.0962	$561.09	$561.10	$561.20