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	$36.45	12.269%	$40.9221	$40.92	$40.90	$40.90
Purchase #2	$136.54	13.386%	$154.8172	$154.82	$154.80	$154.80
Purchase #3	$126.94	4.808%	$133.0433	$133.04	$133.05	$133.00
Purchase #4	$95.48	13.817%	$108.6725	$108.67	$108.65	$108.70
Purchase #5	$40.57	4.137%	$42.2484	$42.25	$42.25	$42.20
Purchase #6	$250.57	11.126%	$278.4484	$278.45	$278.45	$278.40
Purchase #7	$6.60	10.253%	$7.2767	$7.28	$7.30	$7.30
7 purchase totals =	$693.15		$765.4286	$765.43	$765.40	$765.30