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	$236.83	8.432%	$256.7995	$256.80	$256.80	$256.80
Purchase #2	$119.70	5.271%	$126.0094	$126.01	$126.00	$126.00
Purchase #3	$182.33	7.628%	$196.2381	$196.24	$196.25	$196.20
Purchase #4	$90.93	9.152%	$99.2519	$99.25	$99.25	$99.30
Purchase #5	$81.78	11.245%	$90.9762	$90.98	$91.00	$91.00
Purchase #6	$45.88	11.657%	$51.2282	$51.23	$51.25	$51.20
Purchase #7	$47.95	9.487%	$52.499	$52.50	$52.50	$52.50
7 purchase totals =	$805.40		$873.0023	$873.01	$873.05	$873.00