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 $62.85   13.663%   $71.4372   $71.44   $71.45   $71.40  
  Purchase #2 $165.36   3.507%   $171.1592   $171.16   $171.15   $171.20  
  Purchase #3 $170.81   11.241%   $190.0108   $190.01   $190.00   $190.00  
  Purchase #4 $85.55   8.761%   $93.045   $93.05   $93.05   $93.00  
  Purchase #5 $86.45   8.576%   $93.864   $93.86   $93.85   $93.90  
  Purchase #6 $173.80   5.413%   $183.2078   $183.21   $183.20   $183.20  
  Purchase #7 $122.80   10.343%   $135.5012   $135.50   $135.50   $135.50  
  7 purchase totals = $867.62       $938.2252   $938.23   $938.20   $938.20