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	$249.43	8.746%	$271.2451	$271.25	$271.25	$271.20
Purchase #2	$238.25	3.430%	$246.422	$246.42	$246.40	$246.40
Purchase #3	$41.54	9.614%	$45.5337	$45.53	$45.55	$45.50
Purchase #4	$52.79	3.162%	$54.4592	$54.46	$54.45	$54.50
Purchase #5	$136.37	3.812%	$141.5684	$141.57	$141.55	$141.60
Purchase #6	$235.53	8.547%	$255.6607	$255.66	$255.65	$255.70
Purchase #7	$223.37	8.188%	$241.6595	$241.66	$241.65	$241.70
7 purchase totals =	$1,177.28		$1,256.5486	$1,256.55	$1,256.50	$1,256.60