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	$123.31	13.447%	$139.8915	$139.89	$139.90	$139.90
Purchase #2	$69.32	11.571%	$77.341	$77.34	$77.35	$77.30
Purchase #3	$10.83	11.601%	$12.0864	$12.09	$12.10	$12.10
Purchase #4	$31.37	13.395%	$35.572	$35.57	$35.55	$35.60
Purchase #5	$86.66	5.843%	$91.7235	$91.72	$91.70	$91.70
Purchase #6	$72.64	11.845%	$81.2442	$81.24	$81.25	$81.20
Purchase #7	$74.64	5.425%	$78.6892	$78.69	$78.70	$78.70
7 purchase totals =	$468.77		$516.5478	$516.54	$516.55	$516.50