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 $248.79   5.136%   $261.5679   $261.57   $261.55   $261.60  
  Purchase #2 $42.66   9.403%   $46.6713   $46.67   $46.65   $46.70  
  Purchase #3 $233.93   10.309%   $258.0458   $258.05   $258.05   $258.00  
  Purchase #4 $86.71   12.501%   $97.5496   $97.55   $97.55   $97.50  
  Purchase #5 $99.66   7.682%   $107.3159   $107.32   $107.30   $107.30  
  Purchase #6 $191.35   12.483%   $215.2362   $215.24   $215.25   $215.20  
  Purchase #7 $26.27   6.681%   $28.0251   $28.03   $28.05   $28.00  
  7 purchase totals = $929.37       $1,014.4118   $1,014.43   $1,014.40   $1,014.30