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	$227.74	4.768%	$238.5986	$238.60	$238.60	$238.60
Purchase #2	$235.92	9.846%	$259.1487	$259.15	$259.15	$259.10
Purchase #3	$48.92	4.476%	$51.1097	$51.11	$51.10	$51.10
Purchase #4	$47.98	13.200%	$54.3134	$54.31	$54.30	$54.30
Purchase #5	$245.48	13.836%	$279.4446	$279.44	$279.45	$279.40
Purchase #6	$225.81	8.509%	$245.0242	$245.02	$245.00	$245.00
Purchase #7	$168.47	11.502%	$187.8474	$187.85	$187.85	$187.80
7 purchase totals =	$1,200.32		$1,315.4866	$1,315.48	$1,315.45	$1,315.30