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	$237.40	13.716%	$269.9618	$269.96	$269.95	$270.00
Purchase #2	$80.37	11.488%	$89.6029	$89.60	$89.60	$89.60
Purchase #3	$241.45	13.712%	$274.5576	$274.56	$274.55	$274.60
Purchase #4	$161.98	5.641%	$171.1173	$171.12	$171.10	$171.10
Purchase #5	$71.42	11.436%	$79.5876	$79.59	$79.60	$79.60
Purchase #6	$126.30	9.128%	$137.8287	$137.83	$137.85	$137.80
Purchase #7	$133.83	13.602%	$152.0336	$152.03	$152.05	$152.00
7 purchase totals =	$1,052.75		$1,174.6895	$1,174.69	$1,174.70	$1,174.70