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 $212.72   13.553%   $241.5499   $241.55   $241.55   $241.50  
  Purchase #2 $202.75   10.159%   $223.3474   $223.35   $223.35   $223.30  
  Purchase #3 $141.76   11.293%   $157.769   $157.77   $157.75   $157.80  
  Purchase #4 $164.31   6.415%   $174.8505   $174.85   $174.85   $174.90  
  Purchase #5 $40.37   11.304%   $44.9334   $44.93   $44.95   $44.90  
  Purchase #6 $25.49   5.619%   $26.9223   $26.92   $26.90   $26.90  
  Purchase #7 $129.91   12.585%   $146.2592   $146.26   $146.25   $146.30  
  7 purchase totals = $917.31       $1,015.6317   $1,015.63   $1,015.60   $1,015.60