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	$25.89	6.602%	$27.5993	$27.60	$27.60	$27.60
Purchase #2	$73.85	13.642%	$83.9246	$83.92	$83.90	$83.90
Purchase #3	$29.92	6.751%	$31.9399	$31.94	$31.95	$31.90
Purchase #4	$179.70	11.797%	$200.8992	$200.90	$200.90	$200.90
Purchase #5	$172.47	5.526%	$182.0007	$182.00	$182.00	$182.00
Purchase #6	$104.42	9.871%	$114.7273	$114.73	$114.75	$114.70
Purchase #7	$127.25	7.301%	$136.5405	$136.54	$136.55	$136.50
7 purchase totals =	$713.50		$777.6315	$777.63	$777.65	$777.50