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	$180.44	8.696%	$196.1311	$196.13	$196.15	$196.10
Purchase #2	$47.31	7.755%	$50.9789	$50.98	$51.00	$51.00
Purchase #3	$112.46	12.438%	$126.4478	$126.45	$126.45	$126.40
Purchase #4	$53.50	9.219%	$58.4322	$58.43	$58.45	$58.40
Purchase #5	$38.48	4.844%	$40.344	$40.34	$40.35	$40.30
Purchase #6	$135.83	5.860%	$143.7896	$143.79	$143.80	$143.80
Purchase #7	$12.94	12.358%	$14.5391	$14.54	$14.55	$14.50
7 purchase totals =	$580.96		$630.6627	$630.66	$630.75	$630.50