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	$104.67	11.104%	$116.2926	$116.29	$116.30	$116.30
Purchase #2	$31.81	8.299%	$34.4499	$34.45	$34.45	$34.40
Purchase #3	$223.82	12.743%	$252.3414	$252.34	$252.35	$252.30
Purchase #4	$136.69	10.371%	$150.8661	$150.87	$150.85	$150.90
Purchase #5	$108.88	7.614%	$117.1701	$117.17	$117.15	$117.20
Purchase #6	$121.40	8.315%	$131.4944	$131.49	$131.50	$131.50
Purchase #7	$88.98	11.531%	$99.2403	$99.24	$99.25	$99.20
7 purchase totals =	$816.25		$901.8548	$901.85	$901.85	$901.80