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	$84.84	5.736%	$89.7064	$89.71	$89.70	$89.70
Purchase #2	$127.78	11.857%	$142.9309	$142.93	$142.95	$142.90
Purchase #3	$199.87	13.612%	$227.0763	$227.08	$227.10	$227.10
Purchase #4	$103.64	10.397%	$114.4155	$114.42	$114.40	$114.40
Purchase #5	$17.78	8.136%	$19.2266	$19.23	$19.25	$19.20
Purchase #6	$169.46	12.673%	$190.9357	$190.94	$190.95	$190.90
Purchase #7	$137.41	8.632%	$149.2712	$149.27	$149.25	$149.30
7 purchase totals =	$840.78		$933.5626	$933.58	$933.60	$933.50