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	$17.31	7.575%	$18.6212	$18.62	$18.60	$18.60
Purchase #2	$73.61	9.572%	$80.6559	$80.66	$80.65	$80.70
Purchase #3	$42.52	7.210%	$45.5857	$45.59	$45.60	$45.60
Purchase #4	$228.74	5.341%	$240.957	$240.96	$240.95	$241.00
Purchase #5	$94.91	8.544%	$103.0191	$103.02	$103.00	$103.00
Purchase #6	$226.67	12.826%	$255.7427	$255.74	$255.75	$255.70
Purchase #7	$245.92	4.106%	$256.0175	$256.02	$256.00	$256.00
7 purchase totals =	$929.68		$1,000.5991	$1,000.61	$1,000.55	$1,000.60