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 $109.82   13.550%   $124.7006   $124.70   $124.70   $124.70  
  Purchase #2 $152.83   6.134%   $162.2046   $162.20   $162.20   $162.20  
  Purchase #3 $217.38   11.243%   $241.82   $241.82   $241.80   $241.80  
  Purchase #4 $245.48   6.622%   $261.7357   $261.74   $261.75   $261.70  
  Purchase #5 $51.38   7.225%   $55.0922   $55.09   $55.10   $55.10  
  Purchase #6 $210.92   5.601%   $222.7336   $222.73   $222.75   $222.70  
  Purchase #7 $59.36   3.164%   $61.2382   $61.24   $61.25   $61.20  
  7 purchase totals = $1,047.17       $1,129.5249   $1,129.52   $1,129.55   $1,129.40