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 $87.46   6.517%   $93.1598   $93.16   $93.15   $93.20  
  Purchase #2 $106.63   8.284%   $115.4632   $115.46   $115.45   $115.50  
  Purchase #3 $212.59   13.646%   $241.6   $241.60   $241.60   $241.60  
  Purchase #4 $85.58   7.782%   $92.2398   $92.24   $92.25   $92.20  
  Purchase #5 $28.55   5.629%   $30.1571   $30.16   $30.15   $30.20  
  Purchase #6 $201.49   4.190%   $209.9324   $209.93   $209.95   $209.90  
  Purchase #7 $188.68   13.728%   $214.582   $214.58   $214.60   $214.60  
  7 purchase totals = $910.98       $997.1343   $997.13   $997.15   $997.20