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	$16.39	9.328%	$17.9189	$17.92	$17.90	$17.90
Purchase #2	$93.94	12.458%	$105.643	$105.64	$105.65	$105.60
Purchase #3	$120.63	4.652%	$126.2417	$126.24	$126.25	$126.20
Purchase #4	$244.92	10.453%	$270.5215	$270.52	$270.50	$270.50
Purchase #5	$93.66	12.437%	$105.3085	$105.31	$105.30	$105.30
Purchase #6	$106.89	9.345%	$116.8789	$116.88	$116.90	$116.90
Purchase #7	$117.64	4.680%	$123.1456	$123.15	$123.15	$123.10
7 purchase totals =	$794.07		$865.6581	$865.66	$865.65	$865.50