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	$166.98	3.172%	$172.2766	$172.28	$172.30	$172.30
Purchase #2	$92.29	6.819%	$98.5833	$98.58	$98.60	$98.60
Purchase #3	$139.78	7.380%	$150.0958	$150.10	$150.10	$150.10
Purchase #4	$54.81	10.513%	$60.5722	$60.57	$60.55	$60.60
Purchase #5	$63.72	4.200%	$66.3962	$66.40	$66.40	$66.40
Purchase #6	$61.81	9.269%	$67.5392	$67.54	$67.55	$67.50
Purchase #7	$231.57	13.541%	$262.9269	$262.93	$262.95	$262.90
7 purchase totals =	$810.96		$878.3902	$878.40	$878.45	$878.40