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 $248.65   5.339%   $261.9254   $261.93   $261.95   $261.90  
  Purchase #2 $125.34   10.454%   $138.443   $138.44   $138.45   $138.40  
  Purchase #3 $12.80   9.339%   $13.9954   $14.00   $14.00   $14.00  
  Purchase #4 $64.96   11.215%   $72.2453   $72.25   $72.25   $72.20  
  Purchase #5 $67.98   12.518%   $76.4897   $76.49   $76.50   $76.50  
  Purchase #6 $70.37   9.334%   $76.9383   $76.94   $76.95   $76.90  
  Purchase #7 $181.33   3.295%   $187.3048   $187.30   $187.30   $187.30  
  7 purchase totals = $771.43       $827.3419   $827.35   $827.40   $827.20