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	$67.90	9.435%	$74.3064	$74.31	$74.30	$74.30
Purchase #2	$88.84	7.342%	$95.3626	$95.36	$95.35	$95.40
Purchase #3	$6.31	11.549%	$7.0387	$7.04	$7.05	$7.00
Purchase #4	$155.47	8.528%	$168.7285	$168.73	$168.75	$168.70
Purchase #5	$146.30	12.405%	$164.4485	$164.45	$164.45	$164.40
Purchase #6	$7.37	6.262%	$7.8315	$7.83	$7.85	$7.80
Purchase #7	$200.89	9.813%	$220.6033	$220.60	$220.60	$220.60
7 purchase totals =	$673.08		$738.3195	$738.32	$738.35	$738.20