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	$19.53	9.517%	$21.3887	$21.39	$21.40	$21.40
Purchase #2	$182.48	6.507%	$194.354	$194.35	$194.35	$194.40
Purchase #3	$99.69	11.835%	$111.4883	$111.49	$111.50	$111.50
Purchase #4	$112.25	13.221%	$127.0906	$127.09	$127.10	$127.10
Purchase #5	$201.89	5.728%	$213.4543	$213.45	$213.45	$213.50
Purchase #6	$47.42	4.420%	$49.516	$49.52	$49.50	$49.50
Purchase #7	$224.50	5.277%	$236.3469	$236.35	$236.35	$236.30
7 purchase totals =	$887.76		$953.6388	$953.64	$953.65	$953.70