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 $59.94   6.150%   $63.6263   $63.63   $63.65   $63.60  
  Purchase #2 $136.89   5.459%   $144.3628   $144.36   $144.35   $144.40  
  Purchase #3 $132.70   4.211%   $138.288   $138.29   $138.30   $138.30  
  Purchase #4 $174.49   9.410%   $190.9095   $190.91   $190.90   $190.90  
  Purchase #5 $57.62   11.872%   $64.4606   $64.46   $64.45   $64.50  
  Purchase #6 $24.50   7.582%   $26.3576   $26.36   $26.35   $26.40  
  Purchase #7 $17.62   11.207%   $19.5947   $19.59   $19.60   $19.60  
  7 purchase totals = $603.76       $647.5995   $647.60   $647.60   $647.70