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	$237.67	5.143%	$249.8934	$249.89	$249.90	$249.90
Purchase #2	$99.48	11.805%	$111.2236	$111.22	$111.20	$111.20
Purchase #3	$124.46	5.552%	$131.37	$131.37	$131.35	$131.40
Purchase #4	$14.69	5.481%	$15.4952	$15.50	$15.50	$15.50
Purchase #5	$191.65	5.324%	$201.8534	$201.85	$201.85	$201.90
Purchase #6	$10.27	12.110%	$11.5137	$11.51	$11.50	$11.50
Purchase #7	$122.89	6.676%	$131.0941	$131.09	$131.10	$131.10
7 purchase totals =	$801.11		$852.4434	$852.43	$852.40	$852.50