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	$19.47	5.271%	$20.4963	$20.50	$20.50	$20.50
Purchase #2	$210.40	11.549%	$234.6991	$234.70	$234.70	$234.70
Purchase #3	$138.52	10.424%	$152.9593	$152.96	$152.95	$153.00
Purchase #4	$63.76	13.393%	$72.2994	$72.30	$72.30	$72.30
Purchase #5	$32.96	13.729%	$37.4851	$37.49	$37.50	$37.50
Purchase #6	$229.75	11.509%	$256.1919	$256.19	$256.20	$256.20
Purchase #7	$82.55	8.755%	$89.7773	$89.78	$89.80	$89.80
7 purchase totals =	$777.41		$863.9084	$863.92	$863.95	$864.00