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	$105.38	11.158%	$117.1383	$117.14	$117.15	$117.10
Purchase #2	$160.90	9.416%	$176.0503	$176.05	$176.05	$176.10
Purchase #3	$96.38	8.771%	$104.8335	$104.83	$104.85	$104.80
Purchase #4	$114.27	12.384%	$128.4212	$128.42	$128.40	$128.40
Purchase #5	$140.87	11.164%	$156.5967	$156.60	$156.60	$156.60
Purchase #6	$45.89	6.496%	$48.871	$48.87	$48.85	$48.90
Purchase #7	$97.64	4.681%	$102.2105	$102.21	$102.20	$102.20
7 purchase totals =	$761.33		$834.1215	$834.12	$834.10	$834.10