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	$18.54	9.506%	$20.3024	$20.30	$20.30	$20.30
Purchase #2	$101.70	3.118%	$104.871	$104.87	$104.85	$104.90
Purchase #3	$103.70	7.600%	$111.5812	$111.58	$111.60	$111.60
Purchase #4	$189.31	8.536%	$205.4695	$205.47	$205.45	$205.50
Purchase #5	$63.72	4.504%	$66.5899	$66.59	$66.60	$66.60
Purchase #6	$180.60	13.825%	$205.568	$205.57	$205.55	$205.60
Purchase #7	$107.27	13.595%	$121.8534	$121.85	$121.85	$121.90
7 purchase totals =	$764.84		$836.2354	$836.23	$836.20	$836.40