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 $183.89   10.636%   $203.4485   $203.45   $203.45   $203.40  
  Purchase #2 $122.93   13.527%   $139.5587   $139.56   $139.55   $139.60  
  Purchase #3 $84.33   5.142%   $88.6662   $88.67   $88.65   $88.70  
  Purchase #4 $45.28   8.856%   $49.29   $49.29   $49.30   $49.30  
  Purchase #5 $223.53   11.600%   $249.4595   $249.46   $249.45   $249.50  
  Purchase #6 $241.80   8.317%   $261.9105   $261.91   $261.90   $261.90  
  Purchase #7 $34.70   3.297%   $35.8441   $35.84   $35.85   $35.80  
  7 purchase totals = $936.46       $1,028.1775   $1,028.18   $1,028.15   $1,028.20