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	$75.46	13.710%	$85.8056	$85.81	$85.80	$85.80
Purchase #2	$94.91	8.384%	$102.8673	$102.87	$102.85	$102.90
Purchase #3	$38.63	10.313%	$42.6139	$42.61	$42.60	$42.60
Purchase #4	$184.73	5.331%	$194.578	$194.58	$194.60	$194.60
Purchase #5	$79.86	3.189%	$82.4067	$82.41	$82.40	$82.40
Purchase #6	$20.55	6.151%	$21.814	$21.81	$21.80	$21.80
Purchase #7	$94.27	5.249%	$99.2182	$99.22	$99.20	$99.20
7 purchase totals =	$588.41		$629.3037	$629.31	$629.25	$629.30