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 $230.48   11.484%   $256.9483   $256.95   $256.95   $256.90  
  Purchase #2 $111.39   10.112%   $122.6538   $122.65   $122.65   $122.70  
  Purchase #3 $13.89   8.655%   $15.0922   $15.09   $15.10   $15.10  
  Purchase #4 $182.40   9.112%   $199.0203   $199.02   $199.00   $199.00  
  Purchase #5 $165.33   5.706%   $174.7637   $174.76   $174.75   $174.80  
  Purchase #6 $70.34   10.721%   $77.8812   $77.88   $77.90   $77.90  
  Purchase #7 $22.66   10.277%   $24.9888   $24.99   $25.00   $25.00  
  7 purchase totals = $796.49       $871.3483   $871.34   $871.35   $871.40