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 $47.92   7.813%   $51.664   $51.66   $51.65   $51.70  
  Purchase #2 $223.39   3.587%   $231.403   $231.40   $231.40   $231.40  
  Purchase #3 $199.38   3.822%   $207.0003   $207.00   $207.00   $207.00  
  Purchase #4 $23.55   9.813%   $25.861   $25.86   $25.85   $25.90  
  Purchase #5 $100.85   10.224%   $111.1609   $111.16   $111.15   $111.20  
  Purchase #6 $250.25   12.822%   $282.3371   $282.34   $282.35   $282.30  
  Purchase #7 $53.62   8.252%   $58.0447   $58.04   $58.05   $58.00  
  7 purchase totals = $898.96       $967.4710   $967.46   $967.45   $967.50