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 $51.33   5.630%   $54.2199   $54.22   $54.20   $54.20  
  Purchase #2 $187.35   8.524%   $203.3197   $203.32   $203.30   $203.30  
  Purchase #3 $59.45   8.671%   $64.6049   $64.60   $64.60   $64.60  
  Purchase #4 $79.81   6.312%   $84.8476   $84.85   $84.85   $84.80  
  Purchase #5 $248.70   5.121%   $261.4359   $261.44   $261.45   $261.40  
  Purchase #6 $154.40   5.189%   $162.4118   $162.41   $162.40   $162.40  
  Purchase #7 $196.34   11.167%   $218.2653   $218.27   $218.25   $218.30  
  7 purchase totals = $977.38       $1,049.1051   $1,049.11   $1,049.05   $1,049.00