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	$24.47	11.648%	$27.3203	$27.32	$27.30	$27.30
Purchase #2	$57.89	7.511%	$62.2381	$62.24	$62.25	$62.20
Purchase #3	$80.59	3.807%	$83.6581	$83.66	$83.65	$83.70
Purchase #4	$224.85	9.238%	$245.6216	$245.62	$245.60	$245.60
Purchase #5	$94.66	11.798%	$105.828	$105.83	$105.85	$105.80
Purchase #6	$176.82	13.406%	$200.5245	$200.52	$200.50	$200.50
Purchase #7	$229.26	4.183%	$238.8499	$238.85	$238.85	$238.80
7 purchase totals =	$888.54		$964.0405	$964.04	$964.00	$963.90