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	$74.77	13.863%	$85.1354	$85.14	$85.15	$85.10
Purchase #2	$137.27	12.248%	$154.0828	$154.08	$154.10	$154.10
Purchase #3	$131.77	9.684%	$144.5306	$144.53	$144.55	$144.50
Purchase #4	$87.30	6.828%	$93.2608	$93.26	$93.25	$93.30
Purchase #5	$183.89	3.301%	$189.9602	$189.96	$189.95	$190.00
Purchase #6	$48.97	7.688%	$52.7348	$52.73	$52.75	$52.70
Purchase #7	$114.82	4.417%	$119.8916	$119.89	$119.90	$119.90
7 purchase totals =	$778.79		$839.5962	$839.59	$839.65	$839.60