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 $161.27   13.346%   $182.7931   $182.79   $182.80   $182.80  
  Purchase #2 $188.48   12.260%   $211.5876   $211.59   $211.60   $211.60  
  Purchase #3 $129.48   10.295%   $142.81   $142.81   $142.80   $142.80  
  Purchase #4 $7.29   12.102%   $8.1722   $8.17   $8.15   $8.20  
  Purchase #5 $146.28   5.691%   $154.6048   $154.60   $154.60   $154.60  
  Purchase #6 $69.83   9.395%   $76.3905   $76.39   $76.40   $76.40  
  Purchase #7 $235.25   9.832%   $258.3798   $258.38   $258.40   $258.40  
  7 purchase totals = $937.88       $1,034.7380   $1,034.73   $1,034.75   $1,034.80