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	$246.65	13.746%	$280.5545	$280.55	$280.55	$280.60
Purchase #2	$141.61	13.183%	$160.2784	$160.28	$160.30	$160.30
Purchase #3	$39.96	12.682%	$45.0277	$45.03	$45.05	$45.00
Purchase #4	$240.91	8.358%	$261.0453	$261.05	$261.05	$261.00
Purchase #5	$91.72	11.367%	$102.1458	$102.15	$102.15	$102.10
Purchase #6	$104.63	12.195%	$117.3896	$117.39	$117.40	$117.40
Purchase #7	$206.72	4.707%	$216.4503	$216.45	$216.45	$216.50
7 purchase totals =	$1,072.20		$1,182.8916	$1,182.90	$1,182.95	$1,182.90