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	$128.49	9.360%	$140.5167	$140.52	$140.50	$140.50
Purchase #2	$178.65	8.563%	$193.9478	$193.95	$193.95	$193.90
Purchase #3	$190.71	9.758%	$209.3195	$209.32	$209.30	$209.30
Purchase #4	$40.34	12.105%	$45.2232	$45.22	$45.20	$45.20
Purchase #5	$38.60	11.590%	$43.0737	$43.07	$43.05	$43.10
Purchase #6	$59.89	3.327%	$61.8825	$61.88	$61.90	$61.90
Purchase #7	$45.60	3.553%	$47.2202	$47.22	$47.20	$47.20
7 purchase totals =	$682.28		$741.1836	$741.18	$741.10	$741.10