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	$231.98	10.753%	$256.9248	$256.92	$256.90	$256.90
Purchase #2	$127.97	9.867%	$140.5968	$140.60	$140.60	$140.60
Purchase #3	$213.29	11.848%	$238.5606	$238.56	$238.55	$238.60
Purchase #4	$241.60	5.747%	$255.4848	$255.48	$255.50	$255.50
Purchase #5	$247.43	12.814%	$279.1357	$279.14	$279.15	$279.10
Purchase #6	$95.85	4.694%	$100.3492	$100.35	$100.35	$100.30
Purchase #7	$59.49	4.797%	$62.3437	$62.34	$62.35	$62.30
7 purchase totals =	$1,217.61		$1,333.3956	$1,333.39	$1,333.40	$1,333.30