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	$36.27	10.310%	$40.0094	$40.01	$40.00	$40.00
Purchase #2	$108.35	4.356%	$113.0697	$113.07	$113.05	$113.10
Purchase #3	$182.86	7.431%	$196.4483	$196.45	$196.45	$196.40
Purchase #4	$111.31	6.495%	$118.5396	$118.54	$118.55	$118.50
Purchase #5	$86.89	9.480%	$95.1272	$95.13	$95.15	$95.10
Purchase #6	$116.50	8.621%	$126.5435	$126.54	$126.55	$126.50
Purchase #7	$144.89	5.534%	$152.9082	$152.91	$152.90	$152.90
7 purchase totals =	$787.07		$842.6459	$842.65	$842.65	$842.50