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	$216.59	8.786%	$235.6196	$235.62	$235.60	$235.60
Purchase #2	$45.63	3.727%	$47.3306	$47.33	$47.35	$47.30
Purchase #3	$142.33	5.409%	$150.0286	$150.03	$150.05	$150.00
Purchase #4	$110.49	11.874%	$123.6096	$123.61	$123.60	$123.60
Purchase #5	$24.79	12.595%	$27.9123	$27.91	$27.90	$27.90
Purchase #6	$157.61	9.426%	$172.4663	$172.47	$172.45	$172.50
Purchase #7	$65.93	6.398%	$70.1482	$70.15	$70.15	$70.10
7 purchase totals =	$763.37		$827.1152	$827.12	$827.10	$827.00