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	$47.89	7.702%	$51.5785	$51.58	$51.60	$51.60
Purchase #2	$247.54	3.445%	$256.0678	$256.07	$256.05	$256.10
Purchase #3	$154.95	8.799%	$168.5841	$168.58	$168.60	$168.60
Purchase #4	$104.59	6.364%	$111.2461	$111.25	$111.25	$111.20
Purchase #5	$119.60	7.592%	$128.68	$128.68	$128.70	$128.70
Purchase #6	$249.25	12.644%	$280.7652	$280.77	$280.75	$280.80
Purchase #7	$88.66	4.712%	$92.8377	$92.84	$92.85	$92.80
7 purchase totals =	$1,012.48		$1,089.7594	$1,089.77	$1,089.80	$1,089.80