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	$65.66	3.373%	$67.8747	$67.87	$67.85	$67.90
Purchase #2	$92.49	9.564%	$101.3357	$101.34	$101.35	$101.30
Purchase #3	$209.53	13.850%	$238.5499	$238.55	$238.55	$238.50
Purchase #4	$225.73	13.574%	$256.3706	$256.37	$256.35	$256.40
Purchase #5	$138.60	5.283%	$145.9222	$145.92	$145.90	$145.90
Purchase #6	$83.83	13.836%	$95.4287	$95.43	$95.45	$95.40
Purchase #7	$209.54	11.438%	$233.5072	$233.51	$233.50	$233.50
7 purchase totals =	$1,025.38		$1,138.9890	$1,138.99	$1,138.95	$1,138.90