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	$20.55	4.221%	$21.4174	$21.42	$21.40	$21.40
Purchase #2	$178.43	5.761%	$188.7094	$188.71	$188.70	$188.70
Purchase #3	$200.50	7.371%	$215.2789	$215.28	$215.30	$215.30
Purchase #4	$105.96	4.239%	$110.4516	$110.45	$110.45	$110.50
Purchase #5	$133.40	10.589%	$147.5257	$147.53	$147.55	$147.50
Purchase #6	$197.86	8.387%	$214.4545	$214.45	$214.45	$214.50
Purchase #7	$153.77	5.381%	$162.0444	$162.04	$162.05	$162.00
7 purchase totals =	$990.47		$1,059.8819	$1,059.88	$1,059.90	$1,059.90