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	$128.35	9.779%	$140.9013	$140.90	$140.90	$140.90
Purchase #2	$241.98	8.503%	$262.5556	$262.56	$262.55	$262.60
Purchase #3	$5.68	13.575%	$6.4511	$6.45	$6.45	$6.50
Purchase #4	$157.78	12.273%	$177.1443	$177.14	$177.15	$177.10
Purchase #5	$100.40	9.365%	$109.8025	$109.80	$109.80	$109.80
Purchase #6	$172.73	13.751%	$196.4821	$196.48	$196.50	$196.50
Purchase #7	$44.29	6.132%	$47.0059	$47.01	$47.00	$47.00
7 purchase totals =	$851.21		$940.3428	$940.34	$940.35	$940.40