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	$26.38	10.646%	$29.1884	$29.19	$29.20	$29.20
Purchase #2	$113.26	13.815%	$128.9069	$128.91	$128.90	$128.90
Purchase #3	$246.73	13.803%	$280.7861	$280.79	$280.80	$280.80
Purchase #4	$170.81	6.429%	$181.7914	$181.79	$181.80	$181.80
Purchase #5	$200.26	11.317%	$222.9234	$222.92	$222.90	$222.90
Purchase #6	$67.87	6.548%	$72.3141	$72.31	$72.30	$72.30
Purchase #7	$92.86	8.705%	$100.9435	$100.94	$100.95	$100.90
7 purchase totals =	$918.17		$1,016.8538	$1,016.85	$1,016.85	$1,016.80