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 $212.34   13.143%   $240.2478   $240.25   $240.25   $240.20  
  Purchase #2 $203.64   8.843%   $221.6479   $221.65   $221.65   $221.60  
  Purchase #3 $96.92   5.716%   $102.4599   $102.46   $102.45   $102.50  
  Purchase #4 $218.41   6.742%   $233.1352   $233.14   $233.15   $233.10  
  Purchase #5 $200.25   8.203%   $216.6765   $216.68   $216.70   $216.70  
  Purchase #6 $107.65   6.252%   $114.3803   $114.38   $114.40   $114.40  
  Purchase #7 $115.54   6.541%   $123.0975   $123.10   $123.10   $123.10  
  7 purchase totals = $1,154.75       $1,251.6451   $1,251.66   $1,251.70   $1,251.60