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	$249.78	9.859%	$274.4058	$274.41	$274.40	$274.40
Purchase #2	$163.99	3.486%	$169.7067	$169.71	$169.70	$169.70
Purchase #3	$234.86	8.828%	$255.5934	$255.59	$255.60	$255.60
Purchase #4	$32.73	3.375%	$33.8346	$33.83	$33.85	$33.80
Purchase #5	$29.61	8.492%	$32.1245	$32.12	$32.10	$32.10
Purchase #6	$141.56	3.806%	$146.9478	$146.95	$146.95	$146.90
Purchase #7	$52.38	4.354%	$54.6606	$54.66	$54.65	$54.70
7 purchase totals =	$904.91		$967.2734	$967.27	$967.25	$967.20