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	$74.35	11.527%	$82.9203	$82.92	$82.90	$82.90
Purchase #2	$183.68	4.196%	$191.3872	$191.39	$191.40	$191.40
Purchase #3	$118.85	4.247%	$123.8976	$123.90	$123.90	$123.90
Purchase #4	$26.30	3.336%	$27.1774	$27.18	$27.20	$27.20
Purchase #5	$241.59	10.806%	$267.6962	$267.70	$267.70	$267.70
Purchase #6	$138.35	13.296%	$156.745	$156.75	$156.75	$156.70
Purchase #7	$64.78	4.871%	$67.9354	$67.94	$67.95	$67.90
7 purchase totals =	$847.90		$917.7591	$917.78	$917.80	$917.70