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 $92.29   13.653%   $104.8904   $104.89   $104.90   $104.90  
  Purchase #2 $187.65   11.351%   $208.9502   $208.95   $208.95   $209.00  
  Purchase #3 $76.43   5.203%   $80.4067   $80.41   $80.40   $80.40  
  Purchase #4 $146.86   8.630%   $159.534   $159.53   $159.55   $159.50  
  Purchase #5 $140.88   8.312%   $152.5899   $152.59   $152.60   $152.60  
  Purchase #6 $8.82   7.199%   $9.455   $9.46   $9.45   $9.50  
  Purchase #7 $71.69   8.332%   $77.6632   $77.66   $77.65   $77.70  
  7 purchase totals = $724.62       $793.4894   $793.49   $793.50   $793.60