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	$36.32	13.650%	$41.2777	$41.28	$41.30	$41.30
Purchase #2	$81.53	6.168%	$86.5588	$86.56	$86.55	$86.60
Purchase #3	$93.78	9.652%	$102.8316	$102.83	$102.85	$102.80
Purchase #4	$54.39	9.241%	$59.4162	$59.42	$59.40	$59.40
Purchase #5	$150.89	3.754%	$156.5544	$156.55	$156.55	$156.60
Purchase #6	$22.91	7.473%	$24.6221	$24.62	$24.60	$24.60
Purchase #7	$248.39	12.746%	$280.0498	$280.05	$280.05	$280.00
7 purchase totals =	$688.21		$751.3106	$751.31	$751.30	$751.30