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	$31.98	6.563%	$34.0788	$34.08	$34.10	$34.10
Purchase #2	$127.57	7.776%	$137.4898	$137.49	$137.50	$137.50
Purchase #3	$24.77	3.545%	$25.6481	$25.65	$25.65	$25.60
Purchase #4	$76.30	3.308%	$78.824	$78.82	$78.80	$78.80
Purchase #5	$98.41	11.421%	$109.6494	$109.65	$109.65	$109.60
Purchase #6	$203.32	6.659%	$216.8591	$216.86	$216.85	$216.90
Purchase #7	$111.77	5.836%	$118.2929	$118.29	$118.30	$118.30
7 purchase totals =	$674.12		$720.8421	$720.84	$720.85	$720.80