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	$66.28	7.112%	$70.9938	$70.99	$71.00	$71.00
Purchase #2	$120.89	5.674%	$127.7493	$127.75	$127.75	$127.70
Purchase #3	$180.26	9.208%	$196.8583	$196.86	$196.85	$196.90
Purchase #4	$163.98	9.397%	$179.3892	$179.39	$179.40	$179.40
Purchase #5	$31.27	7.438%	$33.5959	$33.60	$33.60	$33.60
Purchase #6	$235.25	9.384%	$257.3259	$257.33	$257.35	$257.30
Purchase #7	$96.94	3.249%	$100.0896	$100.09	$100.10	$100.10
7 purchase totals =	$894.87		$966.0020	$966.01	$966.05	$966.00