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	$29.33	8.747%	$31.8955	$31.90	$31.90	$31.90
Purchase #2	$111.48	10.668%	$123.3727	$123.37	$123.35	$123.40
Purchase #3	$49.56	5.722%	$52.3958	$52.40	$52.40	$52.40
Purchase #4	$142.90	8.265%	$154.7107	$154.71	$154.70	$154.70
Purchase #5	$39.73	3.185%	$40.9954	$41.00	$41.00	$41.00
Purchase #6	$227.94	9.622%	$249.8724	$249.87	$249.85	$249.90
Purchase #7	$163.59	9.431%	$179.0182	$179.02	$179.00	$179.00
7 purchase totals =	$764.53		$832.2607	$832.27	$832.20	$832.30