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	$38.57	12.473%	$43.3808	$43.38	$43.40	$43.40
Purchase #2	$211.89	6.784%	$226.2646	$226.26	$226.25	$226.30
Purchase #3	$150.95	11.710%	$168.6262	$168.63	$168.65	$168.60
Purchase #4	$57.58	3.703%	$59.7122	$59.71	$59.70	$59.70
Purchase #5	$81.60	6.620%	$87.0019	$87.00	$87.00	$87.00
Purchase #6	$214.66	9.532%	$235.1214	$235.12	$235.10	$235.10
Purchase #7	$140.46	12.670%	$158.2563	$158.26	$158.25	$158.30
7 purchase totals =	$895.71		$978.3634	$978.36	$978.35	$978.40