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	$138.70	13.103%	$156.8739	$156.87	$156.85	$156.90
Purchase #2	$11.29	6.528%	$12.027	$12.03	$12.05	$12.00
Purchase #3	$161.64	13.219%	$183.0072	$183.01	$183.00	$183.00
Purchase #4	$113.85	12.312%	$127.8672	$127.87	$127.85	$127.90
Purchase #5	$14.59	3.519%	$15.1034	$15.10	$15.10	$15.10
Purchase #6	$123.47	13.423%	$140.0434	$140.04	$140.05	$140.00
Purchase #7	$145.86	10.320%	$160.9128	$160.91	$160.90	$160.90
7 purchase totals =	$709.40		$795.8349	$795.83	$795.80	$795.80