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	$76.77	7.315%	$82.3857	$82.39	$82.40	$82.40
Purchase #2	$71.38	10.135%	$78.6144	$78.61	$78.60	$78.60
Purchase #3	$113.99	11.805%	$127.4465	$127.45	$127.45	$127.40
Purchase #4	$106.98	5.465%	$112.8265	$112.83	$112.85	$112.80
Purchase #5	$162.78	12.544%	$183.1991	$183.20	$183.20	$183.20
Purchase #6	$210.45	4.789%	$220.5285	$220.53	$220.55	$220.50
Purchase #7	$119.51	11.747%	$133.5488	$133.55	$133.55	$133.50
7 purchase totals =	$861.86		$938.5495	$938.56	$938.60	$938.40