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 $54.89   12.843%   $61.9395   $61.94   $61.95   $61.90  
  Purchase #2 $117.46   10.499%   $129.7921   $129.79   $129.80   $129.80  
  Purchase #3 $164.53   13.739%   $187.1348   $187.13   $187.15   $187.10  
  Purchase #4 $232.31   13.128%   $262.8077   $262.81   $262.80   $262.80  
  Purchase #5 $42.56   12.395%   $47.8353   $47.84   $47.85   $47.80  
  Purchase #6 $56.40   11.868%   $63.0936   $63.09   $63.10   $63.10  
  Purchase #7 $141.71   13.751%   $161.1965   $161.20   $161.20   $161.20  
  7 purchase totals = $809.86       $913.7995   $913.80   $913.85   $913.70