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 $103.72   9.527%   $113.6014   $113.60   $113.60   $113.60  
  Purchase #2 $58.87   13.177%   $66.6273   $66.63   $66.65   $66.60  
  Purchase #3 $154.33   11.701%   $172.3882   $172.39   $172.40   $172.40  
  Purchase #4 $181.33   8.492%   $196.7285   $196.73   $196.75   $196.70  
  Purchase #5 $53.45   9.597%   $58.5796   $58.58   $58.60   $58.60  
  Purchase #6 $15.95   11.688%   $17.8142   $17.81   $17.80   $17.80  
  Purchase #7 $58.70   11.211%   $65.2809   $65.28   $65.30   $65.30  
  7 purchase totals = $626.35       $691.0201   $691.02   $691.10   $691.00