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 $62.69   4.800%   $65.6991   $65.70   $65.70   $65.70  
  Purchase #2 $77.31   11.143%   $85.9247   $85.92   $85.90   $85.90  
  Purchase #3 $212.38   6.435%   $226.0467   $226.05   $226.05   $226.00  
  Purchase #4 $231.69   12.860%   $261.4853   $261.49   $261.50   $261.50  
  Purchase #5 $39.45   7.531%   $42.421   $42.42   $42.40   $42.40  
  Purchase #6 $6.74   8.715%   $7.3274   $7.33   $7.35   $7.30  
  Purchase #7 $49.37   4.779%   $51.7294   $51.73   $51.75   $51.70  
  7 purchase totals = $679.63       $740.6336   $740.64   $740.65   $740.50