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	$36.72	11.390%	$40.9024	$40.90	$40.90	$40.90
Purchase #2	$116.85	12.487%	$131.4411	$131.44	$131.45	$131.40
Purchase #3	$67.98	7.643%	$73.1757	$73.18	$73.20	$73.20
Purchase #4	$58.93	10.626%	$65.1919	$65.19	$65.20	$65.20
Purchase #5	$38.39	9.743%	$42.1303	$42.13	$42.15	$42.10
Purchase #6	$29.25	12.244%	$32.8314	$32.83	$32.85	$32.80
Purchase #7	$134.58	3.302%	$139.0238	$139.02	$139.00	$139.00
7 purchase totals =	$482.70		$524.6966	$524.69	$524.75	$524.60