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	$105.52	5.509%	$111.3331	$111.33	$111.35	$111.30
Purchase #2	$43.76	8.498%	$47.4787	$47.48	$47.50	$47.50
Purchase #3	$82.45	10.236%	$90.8896	$90.89	$90.90	$90.90
Purchase #4	$19.87	9.710%	$21.7994	$21.80	$21.80	$21.80
Purchase #5	$228.33	9.535%	$250.1013	$250.10	$250.10	$250.10
Purchase #6	$60.92	4.136%	$63.4397	$63.44	$63.45	$63.40
Purchase #7	$234.27	12.856%	$264.3878	$264.39	$264.40	$264.40
7 purchase totals =	$775.12		$849.4296	$849.43	$849.50	$849.40