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	$25.66	12.427%	$28.8488	$28.85	$28.85	$28.80
Purchase #2	$78.25	12.384%	$87.9405	$87.94	$87.95	$87.90
Purchase #3	$69.45	13.534%	$78.8494	$78.85	$78.85	$78.80
Purchase #4	$47.51	8.420%	$51.5103	$51.51	$51.50	$51.50
Purchase #5	$124.80	13.634%	$141.8152	$141.82	$141.80	$141.80
Purchase #6	$236.62	8.839%	$257.5348	$257.53	$257.55	$257.50
Purchase #7	$85.54	11.834%	$95.6628	$95.66	$95.65	$95.70
7 purchase totals =	$667.83		$742.1618	$742.16	$742.15	$742.00