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	$40.34	9.650%	$44.2328	$44.23	$44.25	$44.20
Purchase #2	$15.36	9.678%	$16.8465	$16.85	$16.85	$16.80
Purchase #3	$196.50	13.336%	$222.7052	$222.71	$222.70	$222.70
Purchase #4	$39.57	3.292%	$40.8726	$40.87	$40.85	$40.90
Purchase #5	$41.86	4.105%	$43.5784	$43.58	$43.60	$43.60
Purchase #6	$65.87	9.243%	$71.9584	$71.96	$71.95	$72.00
Purchase #7	$89.46	12.547%	$100.6845	$100.68	$100.70	$100.70
7 purchase totals =	$488.96		$540.8784	$540.88	$540.90	$540.90