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 $96.85   8.147%   $104.7404   $104.74   $104.75   $104.70  
  Purchase #2 $57.69   10.411%   $63.6961   $63.70   $63.70   $63.70  
  Purchase #3 $40.68   4.697%   $42.5907   $42.59   $42.60   $42.60  
  Purchase #4 $86.45   12.637%   $97.3747   $97.37   $97.35   $97.40  
  Purchase #5 $78.45   5.844%   $83.0346   $83.03   $83.05   $83.00  
  Purchase #6 $237.96   8.369%   $257.8749   $257.87   $257.85   $257.90  
  Purchase #7 $46.29   8.517%   $50.2325   $50.23   $50.25   $50.20  
  7 purchase totals = $644.37       $699.5439   $699.53   $699.55   $699.50