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 $238.39   11.766%   $266.439   $266.44   $266.45   $266.40  
  Purchase #2 $113.78   8.731%   $123.7141   $123.71   $123.70   $123.70  
  Purchase #3 $94.42   8.214%   $102.1757   $102.18   $102.20   $102.20  
  Purchase #4 $249.96   13.861%   $284.607   $284.61   $284.60   $284.60  
  Purchase #5 $156.70   8.247%   $169.623   $169.62   $169.60   $169.60  
  Purchase #6 $144.77   11.832%   $161.8992   $161.90   $161.90   $161.90  
  Purchase #7 $31.64   11.824%   $35.3811   $35.38   $35.40   $35.40  
  7 purchase totals = $1,029.66       $1,143.8391   $1,143.84   $1,143.85   $1,143.80