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	$13.50	11.719%	$15.0821	$15.08	$15.10	$15.10
Purchase #2	$183.75	7.154%	$196.8955	$196.90	$196.90	$196.90
Purchase #3	$37.29	10.631%	$41.2543	$41.25	$41.25	$41.30
Purchase #4	$36.89	10.715%	$40.8428	$40.84	$40.85	$40.80
Purchase #5	$132.93	11.684%	$148.4615	$148.46	$148.45	$148.50
Purchase #6	$81.36	12.526%	$91.5512	$91.55	$91.55	$91.60
Purchase #7	$186.80	8.680%	$203.0142	$203.01	$203.00	$203.00
7 purchase totals =	$672.52		$737.1016	$737.09	$737.10	$737.20