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	$60.69	7.862%	$65.4614	$65.46	$65.45	$65.50
Purchase #2	$121.59	12.553%	$136.8532	$136.85	$136.85	$136.90
Purchase #3	$89.57	12.702%	$100.9472	$100.95	$100.95	$100.90
Purchase #4	$119.55	3.618%	$123.8753	$123.88	$123.90	$123.90
Purchase #5	$224.65	10.236%	$247.6452	$247.65	$247.65	$247.60
Purchase #6	$175.96	9.391%	$192.4844	$192.48	$192.50	$192.50
Purchase #7	$20.64	8.440%	$22.382	$22.38	$22.40	$22.40
7 purchase totals =	$812.65		$889.6487	$889.65	$889.70	$889.70