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	$18.90	11.836%	$21.137	$21.14	$21.15	$21.10
Purchase #2	$208.27	11.131%	$231.4525	$231.45	$231.45	$231.50
Purchase #3	$118.34	10.797%	$131.1172	$131.12	$131.10	$131.10
Purchase #4	$176.53	12.451%	$198.5098	$198.51	$198.50	$198.50
Purchase #5	$110.96	11.185%	$123.3709	$123.37	$123.35	$123.40
Purchase #6	$173.93	11.591%	$194.0902	$194.09	$194.10	$194.10
Purchase #7	$31.94	6.116%	$33.8935	$33.89	$33.90	$33.90
7 purchase totals =	$838.87		$933.5711	$933.57	$933.55	$933.60