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	$215.62	11.382%	$240.1619	$240.16	$240.15	$240.20
Purchase #2	$168.55	13.759%	$191.7408	$191.74	$191.75	$191.70
Purchase #3	$249.89	12.436%	$280.9663	$280.97	$280.95	$281.00
Purchase #4	$72.26	10.466%	$79.8227	$79.82	$79.80	$79.80
Purchase #5	$241.79	6.260%	$256.9261	$256.93	$256.95	$256.90
Purchase #6	$55.82	6.380%	$59.3813	$59.38	$59.40	$59.40
Purchase #7	$29.97	11.714%	$33.4807	$33.48	$33.50	$33.50
7 purchase totals =	$1,033.90		$1,142.4798	$1,142.48	$1,142.50	$1,142.50