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	$67.75	12.855%	$76.4593	$76.46	$76.45	$76.50
Purchase #2	$246.38	11.157%	$273.8686	$273.87	$273.85	$273.90
Purchase #3	$10.27	12.247%	$11.5278	$11.53	$11.55	$11.50
Purchase #4	$90.53	13.130%	$102.4166	$102.42	$102.40	$102.40
Purchase #5	$24.41	3.491%	$25.2622	$25.26	$25.25	$25.30
Purchase #6	$244.43	4.554%	$255.5613	$255.56	$255.55	$255.60
Purchase #7	$229.28	10.707%	$253.829	$253.83	$253.85	$253.80
7 purchase totals =	$913.05		$998.9248	$998.93	$998.90	$999.00