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 $53.46   13.332%   $60.5873   $60.59   $60.60   $60.60  
  Purchase #2 $209.66   4.490%   $219.0737   $219.07   $219.05   $219.10  
  Purchase #3 $140.55   3.472%   $145.4299   $145.43   $145.45   $145.40  
  Purchase #4 $242.32   10.154%   $266.9252   $266.93   $266.95   $266.90  
  Purchase #5 $109.48   4.588%   $114.5029   $114.50   $114.50   $114.50  
  Purchase #6 $168.45   5.336%   $177.4385   $177.44   $177.45   $177.40  
  Purchase #7 $241.56   6.280%   $256.73   $256.73   $256.75   $256.70  
  7 purchase totals = $1,165.48       $1,240.6875   $1,240.69   $1,240.75   $1,240.60