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	$53.85	4.395%	$56.2167	$56.22	$56.20	$56.20
Purchase #2	$34.63	4.826%	$36.3012	$36.30	$36.30	$36.30
Purchase #3	$246.29	11.397%	$274.3597	$274.36	$274.35	$274.40
Purchase #4	$126.59	13.334%	$143.4695	$143.47	$143.45	$143.50
Purchase #5	$33.67	8.208%	$36.4336	$36.43	$36.45	$36.40
Purchase #6	$45.95	5.573%	$48.5108	$48.51	$48.50	$48.50
Purchase #7	$38.31	13.850%	$43.6159	$43.62	$43.60	$43.60
7 purchase totals =	$579.29		$638.9074	$638.91	$638.85	$638.90