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	$150.55	6.824%	$160.8235	$160.82	$160.80	$160.80
Purchase #2	$35.65	13.257%	$40.3761	$40.38	$40.40	$40.40
Purchase #3	$90.49	5.623%	$95.5783	$95.58	$95.60	$95.60
Purchase #4	$143.89	8.699%	$156.407	$156.41	$156.40	$156.40
Purchase #5	$94.65	9.325%	$103.4761	$103.48	$103.50	$103.50
Purchase #6	$86.92	4.559%	$90.8827	$90.88	$90.90	$90.90
Purchase #7	$200.82	6.277%	$213.4255	$213.43	$213.45	$213.40
7 purchase totals =	$802.97		$860.9692	$860.98	$861.05	$861.00