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	$32.64	4.856%	$34.225	$34.23	$34.25	$34.20
Purchase #2	$85.66	13.283%	$97.0382	$97.04	$97.05	$97.00
Purchase #3	$33.48	6.232%	$35.5665	$35.57	$35.55	$35.60
Purchase #4	$96.34	11.300%	$107.2264	$107.23	$107.25	$107.20
Purchase #5	$43.54	11.377%	$48.4935	$48.49	$48.50	$48.50
Purchase #6	$54.83	8.540%	$59.5125	$59.51	$59.50	$59.50
Purchase #7	$139.85	4.305%	$145.8705	$145.87	$145.85	$145.90
7 purchase totals =	$486.34		$527.9326	$527.94	$527.95	$527.90