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	$102.63	13.771%	$116.7632	$116.76	$116.75	$116.80
Purchase #2	$250.51	12.117%	$280.8643	$280.86	$280.85	$280.90
Purchase #3	$170.54	5.844%	$180.5064	$180.51	$180.50	$180.50
Purchase #4	$138.54	8.731%	$150.6359	$150.64	$150.65	$150.60
Purchase #5	$41.58	9.833%	$45.6686	$45.67	$45.65	$45.70
Purchase #6	$57.36	13.723%	$65.2315	$65.23	$65.25	$65.20
Purchase #7	$24.93	10.797%	$27.6217	$27.62	$27.60	$27.60
7 purchase totals =	$786.09		$867.2916	$867.29	$867.25	$867.30