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 $63.92   8.633%   $69.4382   $69.44   $69.45   $69.40  
  Purchase #2 $217.37   12.192%   $243.8718   $243.87   $243.85   $243.90  
  Purchase #3 $158.42   4.466%   $165.495   $165.50   $165.50   $165.50  
  Purchase #4 $101.55   12.241%   $113.9807   $113.98   $114.00   $114.00  
  Purchase #5 $59.71   13.312%   $67.6586   $67.66   $67.65   $67.70  
  Purchase #6 $165.97   10.659%   $183.6607   $183.66   $183.65   $183.70  
  Purchase #7 $26.45   13.665%   $30.0644   $30.06   $30.05   $30.10  
  7 purchase totals = $793.39       $874.1694   $874.17   $874.15   $874.30