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 $228.35   9.486%   $250.0113   $250.01   $250.00   $250.00  
  Purchase #2 $141.32   13.477%   $160.3657   $160.37   $160.35   $160.40  
  Purchase #3 $141.64   9.165%   $154.6213   $154.62   $154.60   $154.60  
  Purchase #4 $114.47   3.601%   $118.5921   $118.59   $118.60   $118.60  
  Purchase #5 $177.67   9.782%   $195.0497   $195.05   $195.05   $195.00  
  Purchase #6 $243.38   7.184%   $260.8644   $260.86   $260.85   $260.90  
  Purchase #7 $135.42   5.665%   $143.0915   $143.09   $143.10   $143.10  
  7 purchase totals = $1,182.25       $1,282.5960   $1,282.59   $1,282.55   $1,282.60