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	$135.91	4.182%	$141.5938	$141.59	$141.60	$141.60
Purchase #2	$26.59	12.429%	$29.8949	$29.89	$29.90	$29.90
Purchase #3	$11.92	10.741%	$13.2003	$13.20	$13.20	$13.20
Purchase #4	$39.54	10.109%	$43.5371	$43.54	$43.55	$43.50
Purchase #5	$176.35	11.280%	$196.2423	$196.24	$196.25	$196.20
Purchase #6	$36.87	4.832%	$38.6516	$38.65	$38.65	$38.70
Purchase #7	$205.49	8.209%	$222.3587	$222.36	$222.35	$222.40
7 purchase totals =	$632.67		$685.4787	$685.47	$685.50	$685.50