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	$93.32	4.426%	$97.4503	$97.45	$97.45	$97.50
Purchase #2	$157.62	13.859%	$179.4646	$179.46	$179.45	$179.50
Purchase #3	$95.62	3.582%	$99.0451	$99.05	$99.05	$99.00
Purchase #4	$29.85	4.500%	$31.1933	$31.19	$31.20	$31.20
Purchase #5	$66.72	6.786%	$71.2476	$71.25	$71.25	$71.20
Purchase #6	$247.92	9.769%	$272.1393	$272.14	$272.15	$272.10
Purchase #7	$249.30	12.563%	$280.6196	$280.62	$280.60	$280.60
7 purchase totals =	$940.35		$1,031.1598	$1,031.16	$1,031.15	$1,031.10