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	$33.69	11.249%	$37.4798	$37.48	$37.50	$37.50
Purchase #2	$231.86	6.471%	$246.8637	$246.86	$246.85	$246.90
Purchase #3	$142.25	11.406%	$158.475	$158.48	$158.50	$158.50
Purchase #4	$30.71	9.620%	$33.6643	$33.66	$33.65	$33.70
Purchase #5	$150.95	6.789%	$161.198	$161.20	$161.20	$161.20
Purchase #6	$112.75	4.409%	$117.7211	$117.72	$117.70	$117.70
Purchase #7	$117.89	7.711%	$126.9805	$126.98	$127.00	$127.00
7 purchase totals =	$820.10		$882.3824	$882.38	$882.40	$882.50