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	$28.26	9.285%	$30.8839	$30.88	$30.90	$30.90
Purchase #2	$139.46	5.231%	$146.7552	$146.76	$146.75	$146.80
Purchase #3	$38.99	7.845%	$42.0488	$42.05	$42.05	$42.00
Purchase #4	$9.53	13.308%	$10.7983	$10.80	$10.80	$10.80
Purchase #5	$14.82	4.626%	$15.5056	$15.51	$15.50	$15.50
Purchase #6	$133.81	8.123%	$144.6794	$144.68	$144.70	$144.70
Purchase #7	$40.77	12.514%	$45.872	$45.87	$45.85	$45.90
7 purchase totals =	$405.64		$436.5432	$436.55	$436.55	$436.60