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	$9.37	5.286%	$9.8653	$9.87	$9.85	$9.90
Purchase #2	$114.87	12.221%	$128.9083	$128.91	$128.90	$128.90
Purchase #3	$222.82	11.328%	$248.061	$248.06	$248.05	$248.10
Purchase #4	$90.89	11.750%	$101.5696	$101.57	$101.55	$101.60
Purchase #5	$17.53	13.484%	$19.8937	$19.89	$19.90	$19.90
Purchase #6	$196.83	10.386%	$217.2728	$217.27	$217.25	$217.30
Purchase #7	$106.38	11.227%	$118.3233	$118.32	$118.30	$118.30
7 purchase totals =	$758.69		$843.8940	$843.89	$843.80	$844.00