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 $197.54   5.638%   $208.6773   $208.68   $208.70   $208.70  
  Purchase #2 $95.32   6.679%   $101.6864   $101.69   $101.70   $101.70  
  Purchase #3 $99.54   6.218%   $105.7294   $105.73   $105.75   $105.70  
  Purchase #4 $119.98   13.189%   $135.8042   $135.80   $135.80   $135.80  
  Purchase #5 $246.50   6.238%   $261.8767   $261.88   $261.90   $261.90  
  Purchase #6 $230.90   11.106%   $256.5438   $256.54   $256.55   $256.50  
  Purchase #7 $47.28   6.376%   $50.2946   $50.29   $50.30   $50.30  
  7 purchase totals = $1,037.06       $1,120.6124   $1,120.61   $1,120.70   $1,120.60