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 $58.86   8.202%   $63.6877   $63.69   $63.70   $63.70  
  Purchase #2 $203.85   10.341%   $224.9301   $224.93   $224.95   $224.90  
  Purchase #3 $128.36   8.249%   $138.9484   $138.95   $138.95   $138.90  
  Purchase #4 $85.78   8.793%   $93.3226   $93.32   $93.30   $93.30  
  Purchase #5 $8.48   8.107%   $9.1675   $9.17   $9.15   $9.20  
  Purchase #6 $248.29   12.154%   $278.4672   $278.47   $278.45   $278.50  
  Purchase #7 $21.83   5.638%   $23.0608   $23.06   $23.05   $23.10  
  7 purchase totals = $755.45       $831.5843   $831.59   $831.55   $831.60