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 $86.34   10.821%   $95.6829   $95.68   $95.70   $95.70  
  Purchase #2 $69.93   9.405%   $76.5069   $76.51   $76.50   $76.50  
  Purchase #3 $214.74   6.377%   $228.434   $228.43   $228.45   $228.40  
  Purchase #4 $63.74   7.657%   $68.6206   $68.62   $68.60   $68.60  
  Purchase #5 $122.89   12.632%   $138.4135   $138.41   $138.40   $138.40  
  Purchase #6 $65.48   8.786%   $71.2331   $71.23   $71.25   $71.20  
  Purchase #7 $34.62   12.817%   $39.0572   $39.06   $39.05   $39.10  
  7 purchase totals = $657.74       $717.9482   $717.94   $717.95   $717.90