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 $68.59   4.289%   $71.5318   $71.53   $71.55   $71.50  
  Purchase #2 $249.82   4.808%   $261.8313   $261.83   $261.85   $261.80  
  Purchase #3 $102.67   10.852%   $113.8117   $113.81   $113.80   $113.80  
  Purchase #4 $64.87   5.426%   $68.3898   $68.39   $68.40   $68.40  
  Purchase #5 $207.54   5.307%   $218.5541   $218.55   $218.55   $218.60  
  Purchase #6 $92.51   8.726%   $100.5824   $100.58   $100.60   $100.60  
  Purchase #7 $191.67   5.312%   $201.8515   $201.85   $201.85   $201.90  
  7 purchase totals = $977.67       $1,036.5526   $1,036.54   $1,036.60   $1,036.60