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	$143.57	3.329%	$148.3494	$148.35	$148.35	$148.30
Purchase #2	$97.66	12.347%	$109.7181	$109.72	$109.70	$109.70
Purchase #3	$100.89	12.832%	$113.8362	$113.84	$113.85	$113.80
Purchase #4	$112.89	9.285%	$123.3718	$123.37	$123.35	$123.40
Purchase #5	$119.37	5.632%	$126.0929	$126.09	$126.10	$126.10
Purchase #6	$92.53	13.618%	$105.1307	$105.13	$105.15	$105.10
Purchase #7	$249.78	4.873%	$261.9518	$261.95	$261.95	$262.00
7 purchase totals =	$916.69		$988.4509	$988.45	$988.45	$988.40