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	$28.59	10.302%	$31.5353	$31.54	$31.55	$31.50
Purchase #2	$149.77	7.164%	$160.4995	$160.50	$160.50	$160.50
Purchase #3	$91.71	13.811%	$104.3761	$104.38	$104.40	$104.40
Purchase #4	$187.97	6.464%	$200.1204	$200.12	$200.10	$200.10
Purchase #5	$6.77	10.204%	$7.4608	$7.46	$7.45	$7.50
Purchase #6	$92.63	6.756%	$98.8881	$98.89	$98.90	$98.90
Purchase #7	$246.75	4.371%	$257.5354	$257.54	$257.55	$257.50
7 purchase totals =	$804.19		$860.4156	$860.43	$860.45	$860.40