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	$40.92	6.169%	$43.4444	$43.44	$43.45	$43.40
Purchase #2	$165.76	3.797%	$172.0539	$172.05	$172.05	$172.10
Purchase #3	$134.78	4.609%	$140.992	$140.99	$141.00	$141.00
Purchase #4	$150.98	7.769%	$162.7096	$162.71	$162.70	$162.70
Purchase #5	$85.77	7.684%	$92.3606	$92.36	$92.35	$92.40
Purchase #6	$45.52	8.597%	$49.4334	$49.43	$49.45	$49.40
Purchase #7	$50.45	7.491%	$54.2292	$54.23	$54.25	$54.20
7 purchase totals =	$674.18		$715.2231	$715.21	$715.25	$715.20