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 $114.56   8.874%   $124.7261   $124.73   $124.75   $124.70  
  Purchase #2 $138.47   3.589%   $143.4397   $143.44   $143.45   $143.40  
  Purchase #3 $61.73   9.287%   $67.4629   $67.46   $67.45   $67.50  
  Purchase #4 $198.68   7.462%   $213.5055   $213.51   $213.50   $213.50  
  Purchase #5 $41.57   13.442%   $47.1578   $47.16   $47.15   $47.20  
  Purchase #6 $199.50   13.745%   $226.9213   $226.92   $226.90   $226.90  
  Purchase #7 $163.76   10.366%   $180.7354   $180.74   $180.75   $180.70  
  7 purchase totals = $918.27       $1,003.9487   $1,003.96   $1,003.95   $1,003.90