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	$156.93	9.658%	$172.0863	$172.09	$172.10	$172.10
Purchase #2	$94.30	11.524%	$105.1671	$105.17	$105.15	$105.20
Purchase #3	$140.85	8.626%	$152.9997	$153.00	$153.00	$153.00
Purchase #4	$99.50	13.866%	$113.2967	$113.30	$113.30	$113.30
Purchase #5	$242.88	3.318%	$250.9388	$250.94	$250.95	$250.90
Purchase #6	$249.50	12.387%	$280.4056	$280.41	$280.40	$280.40
Purchase #7	$185.67	11.225%	$206.5115	$206.51	$206.50	$206.50
7 purchase totals =	$1,169.63		$1,281.4057	$1,281.42	$1,281.40	$1,281.40