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	$34.75	8.841%	$37.8222	$37.82	$37.80	$37.80
Purchase #2	$5.51	5.768%	$5.8278	$5.83	$5.85	$5.80
Purchase #3	$200.43	7.362%	$215.1857	$215.19	$215.20	$215.20
Purchase #4	$18.72	12.732%	$21.1034	$21.10	$21.10	$21.10
Purchase #5	$25.66	8.634%	$27.8755	$27.88	$27.90	$27.90
Purchase #6	$121.85	7.869%	$131.4384	$131.44	$131.45	$131.40
Purchase #7	$209.51	8.245%	$226.7841	$226.78	$226.80	$226.80
7 purchase totals =	$616.43		$666.0371	$666.04	$666.10	$666.00