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 $23.93   12.313%   $26.8765   $26.88   $26.90   $26.90  
  Purchase #2 $185.94   6.328%   $197.7063   $197.71   $197.70   $197.70  
  Purchase #3 $233.58   10.779%   $258.7576   $258.76   $258.75   $258.80  
  Purchase #4 $37.73   12.842%   $42.5753   $42.58   $42.60   $42.60  
  Purchase #5 $208.76   7.514%   $224.4462   $224.45   $224.45   $224.40  
  Purchase #6 $133.59   5.245%   $140.5968   $140.60   $140.60   $140.60  
  Purchase #7 $113.63   6.575%   $121.1012   $121.10   $121.10   $121.10  
  7 purchase totals = $937.16       $1,012.0599   $1,012.08   $1,012.10   $1,012.10