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	$49.83	13.443%	$56.5286	$56.53	$56.55	$56.50
Purchase #2	$212.66	12.357%	$238.9384	$238.94	$238.95	$238.90
Purchase #3	$8.98	13.212%	$10.1664	$10.17	$10.15	$10.20
Purchase #4	$205.59	3.627%	$213.0467	$213.05	$213.05	$213.00
Purchase #5	$72.53	7.553%	$78.0082	$78.01	$78.00	$78.00
Purchase #6	$162.31	12.142%	$182.0177	$182.02	$182.00	$182.00
Purchase #7	$75.67	13.151%	$85.6214	$85.62	$85.60	$85.60
7 purchase totals =	$787.57		$864.3274	$864.34	$864.30	$864.20