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	$130.45	7.628%	$140.4007	$140.40	$140.40	$140.40
Purchase #2	$241.89	10.679%	$267.7214	$267.72	$267.70	$267.70
Purchase #3	$100.43	3.339%	$103.7834	$103.78	$103.80	$103.80
Purchase #4	$126.33	8.695%	$137.3144	$137.31	$137.30	$137.30
Purchase #5	$9.91	9.661%	$10.8674	$10.87	$10.85	$10.90
Purchase #6	$155.81	3.688%	$161.5563	$161.56	$161.55	$161.60
Purchase #7	$239.56	7.870%	$258.4134	$258.41	$258.40	$258.40
7 purchase totals =	$1,004.38		$1,080.0570	$1,080.05	$1,080.00	$1,080.10