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	$80.69	7.255%	$86.5441	$86.54	$86.55	$86.50
Purchase #2	$74.81	10.284%	$82.5035	$82.50	$82.50	$82.50
Purchase #3	$227.30	7.382%	$244.0793	$244.08	$244.10	$244.10
Purchase #4	$68.64	7.829%	$74.0138	$74.01	$74.00	$74.00
Purchase #5	$52.67	13.623%	$59.8452	$59.85	$59.85	$59.80
Purchase #6	$11.64	12.585%	$13.1049	$13.10	$13.10	$13.10
Purchase #7	$249.46	12.545%	$280.7548	$280.75	$280.75	$280.80
7 purchase totals =	$765.21		$840.8456	$840.83	$840.85	$840.80