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	$93.57	6.746%	$99.8822	$99.88	$99.90	$99.90
Purchase #2	$166.63	5.536%	$175.8546	$175.85	$175.85	$175.90
Purchase #3	$183.76	3.686%	$190.5334	$190.53	$190.55	$190.50
Purchase #4	$136.64	10.478%	$150.9571	$150.96	$150.95	$151.00
Purchase #5	$111.82	10.524%	$123.5879	$123.59	$123.60	$123.60
Purchase #6	$128.54	9.503%	$140.7552	$140.76	$140.75	$140.80
Purchase #7	$64.92	6.712%	$69.2774	$69.28	$69.30	$69.30
7 purchase totals =	$885.88		$950.8478	$950.85	$950.90	$951.00