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 $183.93   9.311%   $201.0557   $201.06   $201.05   $201.10  
  Purchase #2 $247.27   3.553%   $256.0555   $256.06   $256.05   $256.10  
  Purchase #3 $109.37   3.836%   $113.5654   $113.57   $113.55   $113.60  
  Purchase #4 $54.27   10.555%   $59.9982   $60.00   $60.00   $60.00  
  Purchase #5 $230.49   13.557%   $261.7375   $261.74   $261.75   $261.70  
  Purchase #6 $182.30   8.361%   $197.5421   $197.54   $197.55   $197.50  
  Purchase #7 $139.97   10.425%   $154.5619   $154.56   $154.55   $154.60  
  7 purchase totals = $1,147.60       $1,244.5163   $1,244.53   $1,244.50   $1,244.60