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	$148.42	6.134%	$157.5241	$157.52	$157.50	$157.50
Purchase #2	$40.46	13.224%	$45.8104	$45.81	$45.80	$45.80
Purchase #3	$109.86	9.855%	$120.6867	$120.69	$120.70	$120.70
Purchase #4	$64.88	8.193%	$70.1956	$70.20	$70.20	$70.20
Purchase #5	$39.92	13.403%	$45.2705	$45.27	$45.25	$45.30
Purchase #6	$78.80	6.495%	$83.9181	$83.92	$83.90	$83.90
Purchase #7	$70.71	9.242%	$77.245	$77.25	$77.25	$77.20
7 purchase totals =	$553.05		$600.6504	$600.66	$600.60	$600.60