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	$12.46	6.857%	$13.3144	$13.31	$13.30	$13.30
Purchase #2	$127.30	11.653%	$142.1343	$142.13	$142.15	$142.10
Purchase #3	$236.70	13.677%	$269.0735	$269.07	$269.05	$269.10
Purchase #4	$85.77	9.135%	$93.6051	$93.61	$93.60	$93.60
Purchase #5	$210.39	3.167%	$217.0531	$217.05	$217.05	$217.10
Purchase #6	$198.94	12.605%	$224.0164	$224.02	$224.00	$224.00
Purchase #7	$92.81	8.634%	$100.8232	$100.82	$100.80	$100.80
7 purchase totals =	$964.37		$1,060.0200	$1,060.01	$1,059.95	$1,060.00