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   10.592%   $26.4647   $26.46   $26.45   $26.50  
  Purchase #2 $17.53   9.425%   $19.1822   $19.18   $19.20   $19.20  
  Purchase #3 $201.43   3.111%   $207.6965   $207.70   $207.70   $207.70  
  Purchase #4 $250.32   10.324%   $276.163   $276.16   $276.15   $276.20  
  Purchase #5 $124.55   10.192%   $137.2441   $137.24   $137.25   $137.20  
  Purchase #6 $233.44   9.364%   $255.2993   $255.30   $255.30   $255.30  
  Purchase #7 $117.67   4.483%   $122.9451   $122.95   $122.95   $122.90  
  7 purchase totals = $968.87       $1,044.9949   $1,044.99   $1,045.00   $1,045.00