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 $87.98   8.542%   $95.4953   $95.50   $95.50   $95.50  
  Purchase #2 $166.43   13.517%   $188.9263   $188.93   $188.95   $188.90  
  Purchase #3 $115.85   8.407%   $125.5895   $125.59   $125.60   $125.60  
  Purchase #4 $133.33   6.795%   $142.3898   $142.39   $142.40   $142.40  
  Purchase #5 $28.99   5.151%   $30.4833   $30.48   $30.50   $30.50  
  Purchase #6 $63.32   5.322%   $66.6899   $66.69   $66.70   $66.70  
  Purchase #7 $29.31   9.186%   $32.0024   $32.00   $32.00   $32.00  
  7 purchase totals = $625.21       $681.5765   $681.58   $681.65   $681.60