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	$95.57	9.178%	$104.3414	$104.34	$104.35	$104.30
Purchase #2	$32.38	6.454%	$34.4698	$34.47	$34.45	$34.50
Purchase #3	$155.52	5.588%	$164.2105	$164.21	$164.20	$164.20
Purchase #4	$95.69	6.168%	$101.5922	$101.59	$101.60	$101.60
Purchase #5	$238.95	6.785%	$255.1628	$255.16	$255.15	$255.20
Purchase #6	$83.64	6.310%	$88.9177	$88.92	$88.90	$88.90
Purchase #7	$87.56	7.635%	$94.2452	$94.25	$94.25	$94.20
7 purchase totals =	$789.31		$842.9396	$842.94	$842.90	$842.90