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	$74.58	12.664%	$84.0248	$84.02	$84.00	$84.00
Purchase #2	$141.87	10.208%	$156.3521	$156.35	$156.35	$156.40
Purchase #3	$144.67	10.270%	$159.5276	$159.53	$159.55	$159.50
Purchase #4	$188.32	9.128%	$205.5098	$205.51	$205.50	$205.50
Purchase #5	$77.30	6.720%	$82.4946	$82.49	$82.50	$82.50
Purchase #6	$27.35	6.401%	$29.1007	$29.10	$29.10	$29.10
Purchase #7	$176.52	13.544%	$200.4279	$200.43	$200.45	$200.40
7 purchase totals =	$830.61		$917.4375	$917.43	$917.45	$917.40