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	$13.89	8.714%	$15.1004	$15.10	$15.10	$15.10
Purchase #2	$107.86	3.333%	$111.455	$111.46	$111.45	$111.50
Purchase #3	$105.66	8.133%	$114.2533	$114.25	$114.25	$114.30
Purchase #4	$42.86	13.710%	$48.7361	$48.74	$48.75	$48.70
Purchase #5	$89.86	9.306%	$98.2224	$98.22	$98.20	$98.20
Purchase #6	$93.81	9.703%	$102.9124	$102.91	$102.90	$102.90
Purchase #7	$31.49	12.152%	$35.3167	$35.32	$35.30	$35.30
7 purchase totals =	$485.43		$525.9963	$526.00	$525.95	$526.00