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	$234.60	9.287%	$256.3873	$256.39	$256.40	$256.40
Purchase #2	$225.42	7.293%	$241.8599	$241.86	$241.85	$241.90
Purchase #3	$247.43	7.209%	$265.2672	$265.27	$265.25	$265.30
Purchase #4	$165.40	10.184%	$182.2443	$182.24	$182.25	$182.20
Purchase #5	$98.65	6.767%	$105.3256	$105.33	$105.35	$105.30
Purchase #6	$222.79	10.792%	$246.8335	$246.83	$246.85	$246.80
Purchase #7	$152.35	6.352%	$162.0273	$162.03	$162.05	$162.00
7 purchase totals =	$1,346.64		$1,459.9451	$1,459.95	$1,460.00	$1,459.90