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 $224.90   9.232%   $245.6628   $245.66   $245.65   $245.70  
  Purchase #2 $48.55   5.142%   $51.0464   $51.05   $51.05   $51.00  
  Purchase #3 $177.63   12.677%   $200.1482   $200.15   $200.15   $200.10  
  Purchase #4 $68.84   12.670%   $77.562   $77.56   $77.55   $77.60  
  Purchase #5 $40.37   7.182%   $43.2694   $43.27   $43.25   $43.30  
  Purchase #6 $158.83   9.246%   $173.5154   $173.52   $173.50   $173.50  
  Purchase #7 $101.33   12.377%   $113.8716   $113.87   $113.85   $113.90  
  7 purchase totals = $820.45       $905.0758   $905.08   $905.00   $905.10