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	$113.72	3.109%	$117.2556	$117.26	$117.25	$117.30
Purchase #2	$31.78	3.615%	$32.9288	$32.93	$32.95	$32.90
Purchase #3	$72.64	8.292%	$78.6633	$78.66	$78.65	$78.70
Purchase #4	$43.75	8.273%	$47.3694	$47.37	$47.35	$47.40
Purchase #5	$51.62	10.356%	$56.9658	$56.97	$56.95	$57.00
Purchase #6	$100.49	9.285%	$109.8205	$109.82	$109.80	$109.80
Purchase #7	$143.45	11.241%	$159.5752	$159.58	$159.60	$159.60
7 purchase totals =	$557.45		$602.5786	$602.59	$602.55	$602.70