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	$131.65	6.228%	$139.8492	$139.85	$139.85	$139.80
Purchase #2	$249.33	4.517%	$260.5922	$260.59	$260.60	$260.60
Purchase #3	$110.53	10.553%	$122.1942	$122.19	$122.20	$122.20
Purchase #4	$209.67	6.296%	$222.8708	$222.87	$222.85	$222.90
Purchase #5	$5.78	6.503%	$6.1559	$6.16	$6.15	$6.20
Purchase #6	$187.91	9.237%	$205.2672	$205.27	$205.25	$205.30
Purchase #7	$90.63	11.398%	$100.96	$100.96	$100.95	$101.00
7 purchase totals =	$985.50		$1,057.8895	$1,057.89	$1,057.85	$1,058.00