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 $236.71   7.136%   $253.6016   $253.60   $253.60   $253.60  
  Purchase #2 $22.29   5.569%   $23.5313   $23.53   $23.55   $23.50  
  Purchase #3 $67.76   13.275%   $76.7551   $76.76   $76.75   $76.80  
  Purchase #4 $190.48   5.713%   $201.3621   $201.36   $201.35   $201.40  
  Purchase #5 $146.36   5.603%   $154.5606   $154.56   $154.55   $154.60  
  Purchase #6 $44.84   13.493%   $50.8903   $50.89   $50.90   $50.90  
  Purchase #7 $221.39   8.604%   $240.4384   $240.44   $240.45   $240.40  
  7 purchase totals = $929.83       $1,001.1394   $1,001.14   $1,001.15   $1,001.20