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 $248.50   5.177%   $261.3648   $261.36   $261.35   $261.40  
  Purchase #2 $40.67   13.696%   $46.2402   $46.24   $46.25   $46.20  
  Purchase #3 $59.31   10.791%   $65.7101   $65.71   $65.70   $65.70  
  Purchase #4 $190.68   9.814%   $209.3933   $209.39   $209.40   $209.40  
  Purchase #5 $228.70   10.409%   $252.5054   $252.51   $252.50   $252.50  
  Purchase #6 $104.87   13.117%   $118.6258   $118.63   $118.65   $118.60  
  Purchase #7 $189.75   12.505%   $213.4782   $213.48   $213.50   $213.50  
  7 purchase totals = $1,062.48       $1,167.3178   $1,167.32   $1,167.35   $1,167.30