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	$137.88	9.378%	$150.8104	$150.81	$150.80	$150.80
Purchase #2	$84.93	7.798%	$91.5528	$91.55	$91.55	$91.60
Purchase #3	$123.86	12.145%	$138.9028	$138.90	$138.90	$138.90
Purchase #4	$63.38	9.533%	$69.422	$69.42	$69.40	$69.40
Purchase #5	$242.89	5.452%	$256.1324	$256.13	$256.15	$256.10
Purchase #6	$67.45	7.204%	$72.3091	$72.31	$72.30	$72.30
Purchase #7	$131.96	5.563%	$139.3009	$139.30	$139.30	$139.30
7 purchase totals =	$852.35		$918.4304	$918.42	$918.40	$918.40