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	$59.57	11.571%	$66.4628	$66.46	$66.45	$66.50
Purchase #2	$48.76	11.406%	$54.3216	$54.32	$54.30	$54.30
Purchase #3	$102.95	11.664%	$114.9581	$114.96	$114.95	$115.00
Purchase #4	$28.53	3.330%	$29.48	$29.48	$29.50	$29.50
Purchase #5	$104.53	12.343%	$117.4321	$117.43	$117.45	$117.40
Purchase #6	$102.98	7.237%	$110.4327	$110.43	$110.45	$110.40
Purchase #7	$103.66	9.450%	$113.4559	$113.46	$113.45	$113.50
7 purchase totals =	$550.98		$606.5432	$606.54	$606.55	$606.60