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 $64.46   4.266%   $67.2099   $67.21   $67.20   $67.20  
  Purchase #2 $53.41   11.398%   $59.4977   $59.50   $59.50   $59.50  
  Purchase #3 $226.73   13.643%   $257.6628   $257.66   $257.65   $257.70  
  Purchase #4 $59.34   9.291%   $64.8533   $64.85   $64.85   $64.90  
  Purchase #5 $237.39   9.119%   $259.0376   $259.04   $259.05   $259.00  
  Purchase #6 $121.44   7.608%   $130.6792   $130.68   $130.70   $130.70  
  Purchase #7 $39.89   8.386%   $43.2352   $43.24   $43.25   $43.20  
  7 purchase totals = $802.66       $882.1757   $882.18   $882.20   $882.20