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 $67.90   8.212%   $73.4759   $73.48   $73.50   $73.50  
  Purchase #2 $232.61   11.618%   $259.6346   $259.63   $259.65   $259.60  
  Purchase #3 $123.98   7.710%   $133.5389   $133.54   $133.55   $133.50  
  Purchase #4 $107.77   7.131%   $115.4551   $115.46   $115.45   $115.50  
  Purchase #5 $90.87   7.399%   $97.5935   $97.59   $97.60   $97.60  
  Purchase #6 $209.86   6.850%   $224.2354   $224.24   $224.25   $224.20  
  Purchase #7 $114.36   5.376%   $120.508   $120.51   $120.50   $120.50  
  7 purchase totals = $947.35       $1,024.4414   $1,024.45   $1,024.50   $1,024.40