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	$14.80	4.575%	$15.4771	$15.48	$15.50	$15.50
Purchase #2	$213.33	5.590%	$225.2551	$225.26	$225.25	$225.30
Purchase #3	$121.32	7.231%	$130.0926	$130.09	$130.10	$130.10
Purchase #4	$112.55	6.142%	$119.4628	$119.46	$119.45	$119.50
Purchase #5	$81.81	10.104%	$90.0761	$90.08	$90.10	$90.10
Purchase #6	$224.25	10.799%	$248.4668	$248.47	$248.45	$248.50
Purchase #7	$37.64	10.537%	$41.6061	$41.61	$41.60	$41.60
7 purchase totals =	$805.70		$870.4366	$870.45	$870.45	$870.60