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	$131.72	4.309%	$137.3958	$137.40	$137.40	$137.40
Purchase #2	$82.30	9.804%	$90.3687	$90.37	$90.35	$90.40
Purchase #3	$52.35	9.849%	$57.506	$57.51	$57.50	$57.50
Purchase #4	$122.71	12.722%	$138.3212	$138.32	$138.30	$138.30
Purchase #5	$105.72	7.380%	$113.5221	$113.52	$113.50	$113.50
Purchase #6	$111.27	4.262%	$116.0123	$116.01	$116.00	$116.00
Purchase #7	$180.26	9.103%	$196.6691	$196.67	$196.65	$196.70
7 purchase totals =	$786.33		$849.7952	$849.80	$849.70	$849.80