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	$180.70	5.582%	$190.7867	$190.79	$190.80	$190.80
Purchase #2	$6.60	6.371%	$7.0205	$7.02	$7.00	$7.00
Purchase #3	$173.90	9.866%	$191.057	$191.06	$191.05	$191.10
Purchase #4	$37.34	9.348%	$40.8305	$40.83	$40.85	$40.80
Purchase #5	$56.90	5.210%	$59.8645	$59.86	$59.85	$59.90
Purchase #6	$156.99	10.602%	$173.6341	$173.63	$173.65	$173.60
Purchase #7	$16.31	4.534%	$17.0495	$17.05	$17.05	$17.00
7 purchase totals =	$628.74		$680.2428	$680.24	$680.25	$680.20