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	$127.48	9.746%	$139.9042	$139.90	$139.90	$139.90
Purchase #2	$153.38	4.833%	$160.7929	$160.79	$160.80	$160.80
Purchase #3	$90.47	4.739%	$94.7574	$94.76	$94.75	$94.80
Purchase #4	$228.99	13.268%	$259.3724	$259.37	$259.35	$259.40
Purchase #5	$67.79	7.494%	$72.8702	$72.87	$72.85	$72.90
Purchase #6	$139.56	6.606%	$148.7793	$148.78	$148.80	$148.80
Purchase #7	$19.95	7.509%	$21.448	$21.45	$21.45	$21.40
7 purchase totals =	$827.62		$897.9244	$897.92	$897.90	$898.00