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	$6.67	3.418%	$6.898	$6.90	$6.90	$6.90
Purchase #2	$179.25	8.690%	$194.8268	$194.83	$194.85	$194.80
Purchase #3	$96.37	5.545%	$101.7137	$101.71	$101.70	$101.70
Purchase #4	$80.78	11.351%	$89.9493	$89.95	$89.95	$89.90
Purchase #5	$156.72	7.708%	$168.8	$168.80	$168.80	$168.80
Purchase #6	$93.27	8.247%	$100.962	$100.96	$100.95	$101.00
Purchase #7	$154.78	9.105%	$168.8727	$168.87	$168.85	$168.90
7 purchase totals =	$767.84		$832.0225	$832.02	$832.00	$832.00