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	$92.61	12.794%	$104.4585	$104.46	$104.45	$104.50
Purchase #2	$152.63	7.823%	$164.5702	$164.57	$164.55	$164.60
Purchase #3	$98.34	13.725%	$111.8372	$111.84	$111.85	$111.80
Purchase #4	$67.32	3.552%	$69.7112	$69.71	$69.70	$69.70
Purchase #5	$84.65	11.336%	$94.2459	$94.25	$94.25	$94.20
Purchase #6	$177.99	12.605%	$200.4256	$200.43	$200.45	$200.40
Purchase #7	$226.81	5.495%	$239.2732	$239.27	$239.25	$239.30
7 purchase totals =	$900.35		$984.5218	$984.53	$984.50	$984.50