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	$30.65	12.285%	$34.4154	$34.42	$34.40	$34.40
Purchase #2	$43.92	6.770%	$46.8934	$46.89	$46.90	$46.90
Purchase #3	$41.25	7.365%	$44.2881	$44.29	$44.30	$44.30
Purchase #4	$68.95	3.380%	$71.2805	$71.28	$71.30	$71.30
Purchase #5	$108.79	9.576%	$119.2077	$119.21	$119.20	$119.20
Purchase #6	$29.90	5.238%	$31.4662	$31.47	$31.45	$31.50
Purchase #7	$73.76	4.838%	$77.3285	$77.33	$77.35	$77.30
7 purchase totals =	$397.22		$424.8798	$424.89	$424.90	$424.90