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	$37.59	3.430%	$38.8793	$38.88	$38.90	$38.90
Purchase #2	$74.93	7.342%	$80.4314	$80.43	$80.45	$80.40
Purchase #3	$44.35	13.665%	$50.4104	$50.41	$50.40	$50.40
Purchase #4	$64.26	10.164%	$70.7914	$70.79	$70.80	$70.80
Purchase #5	$114.57	12.176%	$128.52	$128.52	$128.50	$128.50
Purchase #6	$11.38	3.725%	$11.8039	$11.80	$11.80	$11.80
Purchase #7	$153.99	7.498%	$165.5362	$165.54	$165.55	$165.50
7 purchase totals =	$501.07		$546.3726	$546.37	$546.40	$546.30