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 $53.63   12.543%   $60.3568   $60.36   $60.35   $60.40  
  Purchase #2 $213.99   4.794%   $224.2487   $224.25   $224.25   $224.20  
  Purchase #3 $248.57   12.578%   $279.8351   $279.84   $279.85   $279.80  
  Purchase #4 $33.44   13.207%   $37.8564   $37.86   $37.85   $37.90  
  Purchase #5 $190.63   4.320%   $198.8652   $198.87   $198.85   $198.90  
  Purchase #6 $242.58   7.516%   $260.8123   $260.81   $260.80   $260.80  
  Purchase #7 $136.57   7.353%   $146.612   $146.61   $146.60   $146.60  
  7 purchase totals = $1,119.41       $1,208.5865   $1,208.60   $1,208.55   $1,208.60