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	$72.78	8.327%	$78.8404	$78.84	$78.85	$78.80
Purchase #2	$191.43	11.285%	$213.0329	$213.03	$213.05	$213.00
Purchase #3	$60.94	12.290%	$68.4295	$68.43	$68.45	$68.40
Purchase #4	$247.47	3.488%	$256.1018	$256.10	$256.10	$256.10
Purchase #5	$18.93	10.226%	$20.8658	$20.87	$20.85	$20.90
Purchase #6	$205.69	4.715%	$215.3883	$215.39	$215.40	$215.40
Purchase #7	$57.51	13.703%	$65.3906	$65.39	$65.40	$65.40
7 purchase totals =	$854.75		$918.0493	$918.05	$918.10	$918.00