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	$92.89	12.187%	$104.2105	$104.21	$104.20	$104.20
Purchase #2	$42.49	12.623%	$47.8535	$47.85	$47.85	$47.90
Purchase #3	$236.59	12.331%	$265.7639	$265.76	$265.75	$265.80
Purchase #4	$200.66	5.117%	$210.9278	$210.93	$210.95	$210.90
Purchase #5	$100.71	12.804%	$113.6049	$113.60	$113.60	$113.60
Purchase #6	$112.35	3.475%	$116.2542	$116.25	$116.25	$116.30
Purchase #7	$104.25	8.232%	$112.8319	$112.83	$112.85	$112.80
7 purchase totals =	$889.94		$971.4467	$971.43	$971.45	$971.50