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	$247.46	12.297%	$277.8902	$277.89	$277.90	$277.90
Purchase #2	$177.78	5.454%	$187.4761	$187.48	$187.50	$187.50
Purchase #3	$109.66	3.812%	$113.8402	$113.84	$113.85	$113.80
Purchase #4	$116.65	9.236%	$127.4238	$127.42	$127.40	$127.40
Purchase #5	$38.60	4.860%	$40.476	$40.48	$40.50	$40.50
Purchase #6	$232.50	6.177%	$246.8615	$246.86	$246.85	$246.90
Purchase #7	$41.59	10.765%	$46.0672	$46.07	$46.05	$46.10
7 purchase totals =	$964.24		$1,040.0350	$1,040.04	$1,040.05	$1,040.10