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	$97.66	11.806%	$109.1897	$109.19	$109.20	$109.20
Purchase #2	$229.82	13.589%	$261.0502	$261.05	$261.05	$261.10
Purchase #3	$90.60	10.571%	$100.1773	$100.18	$100.20	$100.20
Purchase #4	$138.72	5.578%	$146.4578	$146.46	$146.45	$146.50
Purchase #5	$200.81	3.317%	$207.4709	$207.47	$207.45	$207.50
Purchase #6	$249.46	12.286%	$280.1087	$280.11	$280.10	$280.10
Purchase #7	$94.42	11.592%	$105.3652	$105.37	$105.35	$105.40
7 purchase totals =	$1,101.49		$1,209.8198	$1,209.83	$1,209.80	$1,210.00