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	$10.39	13.679%	$11.8112	$11.81	$11.80	$11.80
Purchase #2	$102.47	12.193%	$114.9642	$114.96	$114.95	$115.00
Purchase #3	$138.83	3.817%	$144.1291	$144.13	$144.15	$144.10
Purchase #4	$54.54	9.163%	$59.5375	$59.54	$59.55	$59.50
Purchase #5	$24.60	3.289%	$25.4091	$25.41	$25.40	$25.40
Purchase #6	$169.39	11.754%	$189.3001	$189.30	$189.30	$189.30
Purchase #7	$161.89	13.509%	$183.7597	$183.76	$183.75	$183.80
7 purchase totals =	$662.11		$728.9109	$728.91	$728.90	$728.90