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	$125.90	11.497%	$140.3747	$140.37	$140.35	$140.40
Purchase #2	$84.79	12.558%	$95.4379	$95.44	$95.45	$95.40
Purchase #3	$241.68	9.741%	$265.222	$265.22	$265.20	$265.20
Purchase #4	$78.60	8.209%	$85.0523	$85.05	$85.05	$85.10
Purchase #5	$245.89	5.678%	$259.8516	$259.85	$259.85	$259.90
Purchase #6	$20.44	7.254%	$21.9227	$21.92	$21.90	$21.90
Purchase #7	$68.88	5.461%	$72.6415	$72.64	$72.65	$72.60
7 purchase totals =	$866.18		$940.5027	$940.49	$940.45	$940.50