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 $61.79   12.107%   $69.2709   $69.27   $69.25   $69.30  
  Purchase #2 $208.71   4.285%   $217.6532   $217.65   $217.65   $217.70  
  Purchase #3 $221.94   4.790%   $232.5709   $232.57   $232.55   $232.60  
  Purchase #4 $232.86   10.306%   $256.8586   $256.86   $256.85   $256.90  
  Purchase #5 $247.82   5.598%   $261.693   $261.69   $261.70   $261.70  
  Purchase #6 $216.81   11.125%   $240.9301   $240.93   $240.95   $240.90  
  Purchase #7 $122.82   5.653%   $129.763   $129.76   $129.75   $129.80  
  7 purchase totals = $1,312.75       $1,408.7397   $1,408.73   $1,408.70   $1,408.90