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	$229.80	7.162%	$246.2583	$246.26	$246.25	$246.30
Purchase #2	$215.51	3.189%	$222.3826	$222.38	$222.40	$222.40
Purchase #3	$81.59	6.381%	$86.7963	$86.80	$86.80	$86.80
Purchase #4	$178.50	12.359%	$200.5608	$200.56	$200.55	$200.60
Purchase #5	$91.57	11.817%	$102.3908	$102.39	$102.40	$102.40
Purchase #6	$56.60	10.381%	$62.4756	$62.48	$62.50	$62.50
Purchase #7	$19.49	10.448%	$21.5263	$21.53	$21.55	$21.50
7 purchase totals =	$873.06		$942.3907	$942.40	$942.45	$942.50