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	$146.78	13.302%	$166.3047	$166.30	$166.30	$166.30
Purchase #2	$31.88	8.206%	$34.4961	$34.50	$34.50	$34.50
Purchase #3	$142.90	3.635%	$148.0944	$148.09	$148.10	$148.10
Purchase #4	$116.90	11.652%	$130.5212	$130.52	$130.50	$130.50
Purchase #5	$27.44	5.715%	$29.0082	$29.01	$29.00	$29.00
Purchase #6	$109.88	12.394%	$123.4985	$123.50	$123.50	$123.50
Purchase #7	$179.54	12.812%	$202.5427	$202.54	$202.55	$202.50
7 purchase totals =	$755.32		$834.4658	$834.46	$834.45	$834.40