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 $249.55   7.498%   $268.2613   $268.26   $268.25   $268.30  
  Purchase #2 $192.70   7.641%   $207.4242   $207.42   $207.40   $207.40  
  Purchase #3 $100.44   5.425%   $105.8889   $105.89   $105.90   $105.90  
  Purchase #4 $45.40   4.622%   $47.4984   $47.50   $47.50   $47.50  
  Purchase #5 $232.48   6.216%   $246.931   $246.93   $246.95   $246.90  
  Purchase #6 $126.37   5.588%   $133.4316   $133.43   $133.45   $133.40  
  Purchase #7 $70.92   7.335%   $76.122   $76.12   $76.10   $76.10  
  7 purchase totals = $1,017.86       $1,085.5574   $1,085.55   $1,085.55   $1,085.50