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	$123.90	10.676%	$137.1276	$137.13	$137.15	$137.10
Purchase #2	$111.89	11.221%	$124.4452	$124.45	$124.45	$124.40
Purchase #3	$89.70	6.475%	$95.5081	$95.51	$95.50	$95.50
Purchase #4	$74.92	9.754%	$82.2277	$82.23	$82.25	$82.20
Purchase #5	$36.48	3.180%	$37.6401	$37.64	$37.65	$37.60
Purchase #6	$169.63	10.781%	$187.9178	$187.92	$187.90	$187.90
Purchase #7	$217.92	4.206%	$227.0857	$227.09	$227.10	$227.10
7 purchase totals =	$824.44		$891.9522	$891.97	$892.00	$891.80