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	$85.73	10.678%	$94.8842	$94.88	$94.90	$94.90
Purchase #2	$136.95	11.849%	$153.1772	$153.18	$153.20	$153.20
Purchase #3	$78.78	4.757%	$82.5276	$82.53	$82.55	$82.50
Purchase #4	$131.94	11.269%	$146.8083	$146.81	$146.80	$146.80
Purchase #5	$30.28	8.428%	$32.832	$32.83	$32.85	$32.80
Purchase #6	$97.69	7.289%	$104.8106	$104.81	$104.80	$104.80
Purchase #7	$207.87	6.140%	$220.6332	$220.63	$220.65	$220.60
7 purchase totals =	$769.24		$835.6731	$835.67	$835.75	$835.60