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	$234.32	11.478%	$261.2152	$261.22	$261.20	$261.20
Purchase #2	$63.32	3.389%	$65.4659	$65.47	$65.45	$65.50
Purchase #3	$18.25	4.178%	$19.0125	$19.01	$19.00	$19.00
Purchase #4	$103.83	4.598%	$108.6041	$108.60	$108.60	$108.60
Purchase #5	$10.30	9.645%	$11.2934	$11.29	$11.30	$11.30
Purchase #6	$136.43	7.501%	$146.6636	$146.66	$146.65	$146.70
Purchase #7	$51.46	5.142%	$54.1061	$54.11	$54.10	$54.10
7 purchase totals =	$617.91		$666.3608	$666.36	$666.30	$666.40