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	$146.53	8.156%	$158.481	$158.48	$158.50	$158.50
Purchase #2	$26.30	10.760%	$29.1299	$29.13	$29.15	$29.10
Purchase #3	$169.85	7.470%	$182.5378	$182.54	$182.55	$182.50
Purchase #4	$189.43	5.748%	$200.3184	$200.32	$200.30	$200.30
Purchase #5	$34.55	11.747%	$38.6086	$38.61	$38.60	$38.60
Purchase #6	$83.75	12.587%	$94.2916	$94.29	$94.30	$94.30
Purchase #7	$119.25	7.770%	$128.5157	$128.52	$128.50	$128.50
7 purchase totals =	$769.66		$831.8830	$831.89	$831.90	$831.80