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	$70.67	13.602%	$80.2825	$80.28	$80.30	$80.30
Purchase #2	$187.96	6.815%	$200.7695	$200.77	$200.75	$200.80
Purchase #3	$172.70	10.342%	$190.5606	$190.56	$190.55	$190.60
Purchase #4	$248.53	12.678%	$280.0386	$280.04	$280.05	$280.00
Purchase #5	$250.75	5.318%	$264.0849	$264.08	$264.10	$264.10
Purchase #6	$26.96	10.737%	$29.8547	$29.85	$29.85	$29.90
Purchase #7	$58.85	4.311%	$61.387	$61.39	$61.40	$61.40
7 purchase totals =	$1,016.42		$1,106.9778	$1,106.97	$1,107.00	$1,107.10