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 $241.73   8.326%   $261.8564   $261.86   $261.85   $261.90  
  Purchase #2 $50.34   12.147%   $56.4548   $56.45   $56.45   $56.50  
  Purchase #3 $55.49   5.360%   $58.4643   $58.46   $58.45   $58.50  
  Purchase #4 $172.29   5.243%   $181.3232   $181.32   $181.30   $181.30  
  Purchase #5 $167.58   8.729%   $182.2081   $182.21   $182.20   $182.20  
  Purchase #6 $214.68   7.373%   $230.5084   $230.51   $230.50   $230.50  
  Purchase #7 $82.47   11.664%   $92.0893   $92.09   $92.10   $92.10  
  7 purchase totals = $984.58       $1,062.9045   $1,062.90   $1,062.85   $1,063.00