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	$229.72	8.536%	$249.3289	$249.33	$249.35	$249.30
Purchase #2	$80.52	5.660%	$85.0774	$85.08	$85.10	$85.10
Purchase #3	$210.25	5.643%	$222.1144	$222.11	$222.10	$222.10
Purchase #4	$20.83	4.818%	$21.8336	$21.83	$21.85	$21.80
Purchase #5	$124.86	6.715%	$133.2443	$133.24	$133.25	$133.20
Purchase #6	$246.87	9.609%	$270.5917	$270.59	$270.60	$270.60
Purchase #7	$98.36	12.269%	$110.4278	$110.43	$110.45	$110.40
7 purchase totals =	$1,011.41		$1,092.6181	$1,092.61	$1,092.70	$1,092.50