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	$41.64	3.437%	$43.0712	$43.07	$43.05	$43.10
Purchase #2	$80.32	10.658%	$88.8805	$88.88	$88.90	$88.90
Purchase #3	$200.47	8.732%	$217.975	$217.98	$218.00	$218.00
Purchase #4	$141.63	12.168%	$158.8635	$158.86	$158.85	$158.90
Purchase #5	$121.35	13.237%	$137.4131	$137.41	$137.40	$137.40
Purchase #6	$240.89	4.346%	$251.3591	$251.36	$251.35	$251.40
Purchase #7	$82.62	3.270%	$85.3217	$85.32	$85.30	$85.30
7 purchase totals =	$908.92		$982.8841	$982.88	$982.85	$983.00