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	$154.31	9.460%	$168.9077	$168.91	$168.90	$168.90
Purchase #2	$63.42	3.680%	$65.7539	$65.75	$65.75	$65.80
Purchase #3	$176.93	3.611%	$183.3189	$183.32	$183.30	$183.30
Purchase #4	$169.97	8.530%	$184.4684	$184.47	$184.45	$184.50
Purchase #5	$250.45	11.721%	$279.8052	$279.81	$279.80	$279.80
Purchase #6	$45.89	8.519%	$49.7994	$49.80	$49.80	$49.80
Purchase #7	$150.64	11.552%	$168.0419	$168.04	$168.05	$168.00
7 purchase totals =	$1,011.61		$1,100.0954	$1,100.10	$1,100.05	$1,100.10