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	$124.78	12.110%	$139.8909	$139.89	$139.90	$139.90
Purchase #2	$21.58	7.340%	$23.164	$23.16	$23.15	$23.20
Purchase #3	$18.66	10.718%	$20.66	$20.66	$20.65	$20.70
Purchase #4	$133.34	7.177%	$142.9098	$142.91	$142.90	$142.90
Purchase #5	$196.60	13.341%	$222.8284	$222.83	$222.85	$222.80
Purchase #6	$68.84	6.513%	$73.3235	$73.32	$73.30	$73.30
Purchase #7	$83.65	12.715%	$94.2861	$94.29	$94.30	$94.30
7 purchase totals =	$647.45		$717.0627	$717.06	$717.05	$717.10