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	$30.66	12.411%	$34.4652	$34.47	$34.45	$34.50
Purchase #2	$81.28	10.308%	$89.6583	$89.66	$89.65	$89.70
Purchase #3	$92.69	5.792%	$98.0586	$98.06	$98.05	$98.10
Purchase #4	$49.77	13.856%	$56.6661	$56.67	$56.65	$56.70
Purchase #5	$55.68	6.792%	$59.4618	$59.46	$59.45	$59.50
Purchase #6	$170.95	13.542%	$194.1	$194.10	$194.10	$194.10
Purchase #7	$70.88	4.221%	$73.8718	$73.87	$73.85	$73.90
7 purchase totals =	$551.91		$606.2818	$606.29	$606.20	$606.50