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	$48.81	11.166%	$54.2601	$54.26	$54.25	$54.30
Purchase #2	$126.63	9.410%	$138.5459	$138.55	$138.55	$138.50
Purchase #3	$91.77	8.868%	$99.9082	$99.91	$99.90	$99.90
Purchase #4	$241.65	6.429%	$257.1857	$257.19	$257.20	$257.20
Purchase #5	$207.32	8.487%	$224.9152	$224.92	$224.90	$224.90
Purchase #6	$123.98	7.619%	$133.426	$133.43	$133.45	$133.40
Purchase #7	$83.73	6.524%	$89.1925	$89.19	$89.20	$89.20
7 purchase totals =	$923.89		$997.4336	$997.45	$997.45	$997.40