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	$25.87	4.441%	$27.0189	$27.02	$27.00	$27.00
Purchase #2	$129.45	11.626%	$144.4999	$144.50	$144.50	$144.50
Purchase #3	$229.64	9.704%	$251.9243	$251.92	$251.90	$251.90
Purchase #4	$122.66	12.561%	$138.0673	$138.07	$138.05	$138.10
Purchase #5	$70.48	11.789%	$78.7889	$78.79	$78.80	$78.80
Purchase #6	$20.50	4.396%	$21.4012	$21.40	$21.40	$21.40
Purchase #7	$35.98	7.824%	$38.7951	$38.80	$38.80	$38.80
7 purchase totals =	$634.58		$700.4956	$700.50	$700.45	$700.50