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	$129.76	12.704%	$146.2447	$146.24	$146.25	$146.20
Purchase #2	$33.40	4.461%	$34.89	$34.89	$34.90	$34.90
Purchase #3	$154.57	6.378%	$164.4285	$164.43	$164.45	$164.40
Purchase #4	$18.63	5.133%	$19.5863	$19.59	$19.60	$19.60
Purchase #5	$163.83	6.822%	$175.0065	$175.01	$175.00	$175.00
Purchase #6	$107.32	4.514%	$112.1644	$112.16	$112.15	$112.20
Purchase #7	$16.40	13.456%	$18.6068	$18.61	$18.60	$18.60
7 purchase totals =	$623.91		$670.9272	$670.93	$670.95	$670.90